Internal combustion engine

ABSTRACT

An internal combustion engine is provided with an exhaust valve which has a tapered plug part, a tube-shaped member which is arranged in a region where the exhaust valve is arranged and which is engaged with the tapered plug part of the exhaust valve at one end part which faces a combustion chamber, and a fluid spring for biasing the tube-shaped member to the side facing the combustion chamber. The tube-shaped member is formed so as to be able to move substantially parallel to the direction of movement of the exhaust valve and the other part abuts against the fluid spring. The fluid spring is formed so as to contract using the change in pressure of the combustion chamber as a drive source when the pressure of the combustion chamber reaches a predetermined control pressure.

TECHNICAL FIELD

The present invention relates to an internal combustion engine.

BACKGROUND ART

An internal combustion engine supplies a combustion chamber with fueland air and burns the fuel in the combustion chamber to output a driveforce. When burning fuel in the combustion chamber, the air-fuel mixtureof the air and fuel is compressed in state. It is known that thecompression ratio of the internal combustion engine has an effect on theoutput and fuel consumption. By raising the compression ratio, it ispossible to increase the output torque or reduce the fuel consumption.

Japanese Patent Publication No. 2000-230439 A1 discloses a self-ignitiontype internal combustion engine which provides a combustion chamber witha sub chamber which is communicated through a pressure regulator,wherein the pressure regulator has a valve element and a valve shaftwhich is connected to the valve element and is biased to the combustionchamber side. It is disclosed that this self igniting type internalcombustion engine pushes up the pressure regulator against the pressureof an elastic member and releases the pressure to the sub chamber whenoverly early ignition etc. causes the combustion pressure to exceed apredetermined allowable pressure value. This publication discloses apressure regulator which operates by a pressure larger than the pressurewhich occurs due to overly early ignition etc. Japanese PatentPublication No. 2006-522895 A1 discloses a piston wherein between thepiston and a connecting shaft, a disk spring is assembled which acts soas to bias the connecting shaft in a direction opposite to the pistoncrown. Further, it discloses that the piston crown moves on an axisrelative to the connecting shaft. It discloses that in this piston, whenthe piston passes top dead center, the energy which had been stored inthe disk spring is released leading to the generation of an outputtorque.

CITATION LIST Patent Literature

-   PLT 1: Japanese Patent Publication No. 2000-230439 A1-   PLT 2: Japanese Patent Publication No. 2006-522895 A1

SUMMARY OF INVENTION Technical Problem

In a spark ignition type of internal combustion engine, a mixture offuel and air is ignited in a combustion chamber by an ignition device,whereby the air-fuel mixture burns and the piston is pushed down. Atthis time, the compression ratio becomes higher, whereby the heatefficiency is improved. In this regard, if raising the compressionratio, sometimes abnormal combustion occurs. For example, self-ignitionsometimes occurs when the compression ratio becomes higher.

To prevent the occurrence of abnormal combustion, the ignition timingcan be retarded. However, by retarding the ignition timing, the outputtorque becomes smaller or the fuel consumption efficiency deteriorates.Further, by retarding the ignition timing, the temperature of theexhaust gas becomes higher. For this reason, sometimes high qualitymaterials become necessary for the component parts of the exhaustpurification device or a device for cooling the exhaust gas becomesnecessary. Furthermore, to lower the temperature of the exhaust gas,sometimes a value of the air-fuel ratio when burning fuel in thecombustion chamber is made less than the stoichiometric air-fuel ratio.That is, sometimes the air-fuel ratio at the time of combustion is maderich. However, there was the problem that when a three-way catalyst isarranged as the exhaust purification device, if the air-fuel ratio ofthe exhaust gas deviates from the stoichiometric air-fuel ratio, thepurification ability ends up becoming smaller and the exhaust gas can nolonger be sufficiently purified.

In the internal combustion engine which is disclosed in the aboveJapanese Patent Publication No. 2000-230439 A1, a space whichcommunicates with the combustion chamber is formed in the cylinder headand a mechanical spring is arranged in this space. However, a passageconnecting to the combustion chamber is formed in the cylinder head, sothe intake valve or the exhaust valve is liable to become smaller.

The above Japanese Patent Publication No. 2006-522895 A1 discloses aninternal combustion engine wherein a mechanical spring is arranged in apiston. However, the mechanical spring which is arranged in the pistonis insufficient in amount of possible deformation. A sufficient strokeis liable to be unable to be secured. For this reason, control of thepressure inside of the cylinder was difficult.

The present invention has as its object the provision of an internalcombustion engine which suppresses the occurrence of abnormalcombustion.

Solution to Problem

An internal combustion engine of the present invention is provided withan on-off valve which has a shaft-shaped part and tapered plug part andis formed to be able to open and close a passage which is communicatedwith a combustion chamber, a support structure which includes a passagewhich communicates with the combustion chamber and which supports theon-off valve, an interposed member which is arranged in a region wherethe on-off valve is arranged in the passage which communicates with thecombustion chamber and which is engaged with the tapered plug part ofthe on-off valve at one end part which faces the combustion chamber, anda spring device for biasing the interposed member to the side whichfaces the combustion chamber. The interposed member is formed to be ableto move substantially parallel to a direction of movement of the on-offvalve and abuts against the spring device at the other end part at theopposite side from the one end part. The spring device is formed so asto contract using the change in pressure of the combustion chamber as adrive source when the pressure of the combustion chamber reaches apredetermined control pressure. When the combustion chamber reaches thecontrol pressure during the time period from the compression stroke tothe expansion stroke of a combustion cycle, the spring devicecontracting causes the tapered plug part and the interposed member tomove toward the outside of the combustion chamber and the combustionchamber to increase in volume.

In the present invention, the internal combustion engine may be providedwith an operating state detecting device which detects an operatingstate of the internal combustion engine and a movement restrictingdevice which restricts the amount of movement of the interposed member,may detect the operating state of the internal combustion engine, mayselect the maximum pressure of the combustion chamber in accordance withthe detected operating state, and may use the selected maximum pressureof the combustion chamber as the basis to restrict the amount ofmovement of the interposed member.

In the present invention, the internal combustion engine may be providedwith a blocking device which blocks at least part of the passage whichcommunicates with the combustion chamber, and the blocking device may beformed so as to promote a circumferential direction flow or an axialdirection flow in the combustion chamber the smaller the flow sectionalarea of the passage which communicates with the combustion chamber. Thesmaller the flow sectional area of the passage which communicates withthe combustion chamber, the smaller the movement restricting devicerestricts the amount of movement of the interposed member and the largerthe maximum pressure of the combustion chamber can be made.

In the present invention, the internal combustion engine may be aninternal combustion engine in which a plurality of on-off valves arearranged for a single combustion chamber, wherein the engine is providedwith a plurality of interposed members and a plurality of spring deviceswhich are arranged corresponding to the plurality of on-off valves andthe plurality of spring devices are formed so that the elastic forcesbecome smaller the larger the total weights of the moving members whichinclude the tapered plug parts and the interposed members.

In the present invention, the shaft-shaped part of the on-off valve mayinclude a first valve shaft part which is connected to the tapered plugpart and a second valve shaft part which is connected to the first valveshaft part through an elastic member, and the elastic member may have anelastic force by which it contracts corresponding to the amount ofcontraction of the spring device when the pressure of the combustionchamber reaches the control pressure and the spring device contracts andhas an elastic force by which it does not contract when opening theon-off valve for opening the passage which communicates with thecombustion chamber.

In the present invention, the internal combustion engine may be providedwith a valve biasing member which biases the on-off valve in a directionby which the on-off valve closes, and the spring device may be arrangedat the inside of the valve biasing member or at the outside so as tosurround the valve biasing member.

In the present invention, the internal combustion engine may be providedwith a cam for driving the on-off valve and a variable valve mechanismwhich changes a phase of the cam relative to a crank angle, the cam mayhave a recessed part which is formed so that the on-off valve can moveduring the time period while the spring device is contracted, and thevariable valve mechanism may be used to change the phase of the recessedpart of the cam so as to restrict the amount of movement of the on-offvalve during the time period while the spring device is contracted.

In the present invention, the internal combustion engine may be providedwith an electromagnetic drive device for driving the on-off valve, andthe electromagnetic drive device may be driven during the time periodwhile the pressure of the combustion chamber reaches the controlpressure so as to adjust the pressure of the combustion chamber.

Advantageous Effects of Invention

According to the present invention, it is possible to provide aninternal combustion engine which suppresses the occurrence of abnormalcombustion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an internal combustion engine inEmbodiment 1.

FIG. 2 is a schematic cross-sectional view of a first combustionpressure control device in Embodiment 1.

FIG. 3 is an enlarged schematic cross-sectional view of a stoppermechanism of a first stem of the first combustion pressure controldevice in Embodiment 1.

FIG. 4 is a schematic cross-sectional view of the time when a fluidspring is contracted in the first combustion pressure control device ofEmbodiment 1.

FIG. 5 is a view which explains the pressure of the combustion chamberand the amount of contraction of the fluid spring in an internalcombustion engine which is provided with the combustion pressure controldevice of Embodiment 1.

FIG. 6 is a graph which explains a relationship between an ignitiontiming and an output torque in a comparative example.

FIG. 7 is a graph which explains a relationship between a crank angleand a pressure of a combustion chamber in a comparative example.

FIG. 8 is a graph which explains a relationship between a load of aninternal combustion engine and a maximum pressure of the combustionchamber in a comparative example.

FIG. 9 is an enlarged view of a graph of the pressure of the combustionchamber when the pressure of the combustion chamber reaches a controlpressure in the first combustion pressure control device of Embodiment1.

FIG. 10 is a graph which explains a graph of the ignition timing of aninternal combustion engine in Embodiment 1 and an internal combustionengine of a comparative example.

FIG. 11 is an enlarged schematic cross-sectional view of a connectingpart of a first stem and a second stem of the second combustion pressurecontrol device in the Embodiment 1.

FIG. 12 is a schematic cross-sectional view of a third combustionpressure control device in Embodiment 1.

FIG. 13 is a schematic cross-sectional view of a fourth combustionpressure control device in Embodiment 1.

FIG. 14 is a schematic cross-sectional view of a first combustionpressure control device in Embodiment 2.

FIG. 15 is a schematic perspective view of a movement restricting deviceand a blocking device of a first combustion pressure control device ofEmbodiment 2.

FIG. 16 is an explanatory view of the movement restricting device of thefirst combustion pressure control device in Embodiment 2.

FIG. 17 is a graph which explains a maximum pressure of a combustionchamber in an internal combustion engine which is provided with thefirst combustion pressure control device of Embodiment 2.

FIG. 18 is a graph which explains a relationship between a speed of aninternal combustion engine and a knocking margin ignition timing in acomparative example.

FIG. 19 is a graph which explains a relationship between a speed and themaximum pressure of the combustion chamber of an internal combustionengine which is provided with the first combustion pressure controldevice in Embodiment 2.

FIG. 20 is a graph which explains a relationship between a concentrationof alcohol which is contained in fuel and an amount of retardationcorrection in a comparative example.

FIG. 21 is a graph which explains a relationship between an alcoholconcentration of fuel and the maximum pressure of a combustion chamberof an internal combustion engine which is provided with the firstcombustion pressure control device of Embodiment 2.

FIG. 22 is a schematic cross-sectional view of a combustion chamber,engine intake passage, and engine exhaust passage of an internalcombustion engine which is provided with the first combustion pressurecontrol device in Embodiment 2.

FIG. 23 is a schematic cross-sectional view of a combustion chamber,engine intake passage, and engine exhaust passage of another internalcombustion engine which is provided with the first combustion pressurecontrol device in Embodiment 2.

FIG. 24 is a schematic perspective view of a movement restricting deviceand a blocking device of a second combustion pressure control device ofEmbodiment 2.

FIG. 25 is a schematic cross-sectional view of an internal combustionengine which is provided with the second combustion pressure controldevice in Embodiment 2.

FIG. 26 is a schematic cross-sectional view of a first combustionpressure control device in Embodiment 3.

FIG. 27 is a schematic cross-sectional view of the part of an exhaustcam and the exhaust valve of the first combustion pressure controldevice in Embodiment 3.

FIG. 28 is a schematic view of a variable valve mechanism which changesthe phase of a cam with respect to a crank angle in Embodiment 3.

FIG. 29 is a schematic cross-sectional view of an exhaust cam of thefirst combustion pressure control device in Embodiment 3.

FIG. 30 is a time chart of operational control of an internal combustionengine which is provided with the first combustion pressure controldevice in Embodiment 3.

FIG. 31 is a schematic perspective view of the part of an exhaust camand the exhaust valve of a second combustion pressure control device inEmbodiment 3.

FIG. 32 is a schematic cross-sectional view of a second exhaust cam ofthe second combustion pressure control device in Embodiment 3.

FIG. 33 is a schematic cross-sectional view of a cam switching device ofthe second combustion pressure control device in Embodiment 3.

FIG. 34 is another schematic cross-sectional view of a cam switchingdevice of the second combustion pressure control device in Embodiment 3.

FIG. 35 is a graph of the pressure of the combustion chamber of aninternal combustion engine which is provided with the second combustionpressure control device in Embodiment 3.

FIG. 36 is a schematic cross-sectional view of a combustion pressurecontrol device in Embodiment 4.

FIG. 37 is a graph of the pressure of the combustion chamber of aninternal combustion engine of a comparative example in Embodiment 4.

FIG. 38 is a time chart of first operational control of the combustionpressure control device in Embodiment 4.

FIG. 39 is a time chart of second operational control of the combustionpressure control device in Embodiment 4.

FIG. 40 is a time chart of third operational control of the combustionpressure control device in Embodiment 4.

DESCRIPTION OF EMBODIMENTS Embodiment 1

Referring to FIG. 1 to FIG. 13, an internal combustion engine inEmbodiment 1 will be explained. In the present embodiment, theexplanation will be given with reference to the example of an internalcombustion engine which is mounted in a vehicle.

FIG. 1 is a schematic view of an internal combustion engine in thepresent embodiment. The internal combustion engine in the presentembodiment is a spark ignition type. The internal combustion engine isprovided with an engine body 1. The engine body 1 includes a cylinderblock 2 and cylinder head 4. Inside the cylinder block 2, pistons 3 arearranged. Each piston 3 reciprocates inside of the cylinder block 2. Inthe present invention, the space inside the cylinder surrounded by thecrown surface of the piston, the cylinder head, the intake valve, andthe exhaust valve when the piston reaches compression top dead centerand the space inside the cylinder surrounded by the crown surface of thepiston at any position, the cylinder head, the intake valve, and theexhaust valve will be called the “combustion chamber”.

A combustion chamber 5 is formed for each cylinder. Each combustionchamber 5 is connected to an engine intake passage and an engine exhaustpassage as passages which communicate with the combustion chamber. Theengine intake passage is a passage for feeding the combustion chamber 5with air or a mixture of fuel and air. The engine exhaust passage is apassage for discharging the exhaust gas which is produced by combustionof fuel in the combustion chamber 5. At the cylinder head 4, an intakeport 7 and exhaust port 9 are formed.

The passages which communicate with the combustion chamber 5 areprovided with on-off valves constituted by an intake valve 6 and exhaustvalve 8. The intake valve 6 is arranged at an end of the intake port 7and is formed to be able to open and close the engine intake passagewhich is communicated with the combustion chamber 5. The exhaust valve 8is arranged at an end of the exhaust port 9 and is formed to be able toopen and close the engine exhaust passage which is communicated with thecombustion chamber 5. The on-off valves are supported by a supportstructure constituted by the cylinder head 4. At the cylinder head 4, aspark plug 10 serving as an ignition device is fastened. The spark plug10 is formed to ignite the fuel in the combustion chamber 5.

The internal combustion engine in the present embodiment is providedwith a fuel injector 11 for feeding fuel to each combustion chamber 5.The fuel injector 11 in the present embodiment is arranged so as toinject fuel to the intake port 7. The fuel injector 11 is not limited tothis. It is sufficient that it be arranged to be able to feed fuel tothe combustion chamber 5. For example, the fuel injector may be arrangedso as to directly inject fuel to the combustion chamber.

The fuel injector 11 is connected to a fuel tank 28 through anelectronic control type variable discharge fuel pump 29. The fuel whichis stored in the fuel tank 28 is supplied to the fuel injector 11 by thefuel pump 29. In the middle of the flow path for feed of fuel, as a fuelproperty detecting device for detecting the properties of the fuel, afuel property sensor 45 is arranged. For example, in an internalcombustion engine which uses fuel which contains alcohol, a fuelproperty sensor 45 constituted by an alcohol concentration sensor isprovided. The fuel property detecting device may also be arranged in thefuel tank.

The intake port 7 of each cylinder is connected through a correspondingintake runner 13 to a surge tank 14. The surge tank 14 is connectedthrough an intake duct 15 and air flow meter 16 to an air cleaner (notshown). At the intake duct 15, the air flow meter 16 is arranged todetect the amount of intake air. At the inside of the intake duct 15, athrottle valve 18 which is driven by a step motor 17 is arranged. On theother hand, the exhaust port 9 of each cylinder is connected to acorresponding exhaust runner 19. The exhaust runner 19 is connected to acatalytic converter 21. The catalytic converter 21 in the presentembodiment includes a three-way catalyst 20. The catalytic converter 21is connected to an exhaust pipe 22. The engine exhaust passage isprovided with a temperature sensor 46 for detecting the temperature ofthe exhaust gas.

The engine body 1 in the present embodiment has a recirculation passagefor exhaust gas recirculation (EGR). In the present embodiment, as therecirculation passage, an EGR gas supply line 26 is arranged. The EGRgas supply line 26 connects an exhaust runner 19 and a surge tank 14each other. The EGR gas supply line 26 is provided with an EGR controlvalve 27. The EGR control valve 27 is formed to enable the flow rate ofthe exhaust gas which is recirculated to be adjusted. If the ratio ofthe air and fuel (hydrocarbons) which are supplied to the engine intakepassage, combustion chamber, or engine exhaust passage is referred to asthe air-fuel ratio (A/F) of the exhaust gas, the engine exhaust passageat the upstream side of the catalyst converter 21 is provided with anair-fuel ratio sensor 47 for detecting the air-fuel ratio of the exhaustgas.

The internal combustion engine in the present embodiment is providedwith an electronic control unit 31. The electronic control unit 31 inthe present embodiment includes a digital computer. The electroniccontrol unit 31 includes components connected to each other through abidirectional bus 32 such as a RAM (random access memory) 33, ROM (readonly memory) 34, CPU (microprocessor) 35, input port 36, and output port37.

The air flow meter 16 generates an output voltage which is proportionalto the amount of intake air which is taken into each combustion chamber5. This output voltage is input to the input port 36 through acorresponding AD converter 38. An accelerator pedal 40 has a load sensor41 connected to it. The load sensor 41 generates an output voltage whichis proportional to the amount of depression of the accelerator pedal 40.This output voltage is input through a corresponding AD converter 38 tothe input port 36. Further, a crank angle sensor 42 generates an outputpulse every time a crankshaft for example turns by 30°. This outputpulse is input to the input port 36. The output of the crank anglesensor 42 may be used to detect the engine speed. Furthermore, theelectronic control unit 31 receives as input signals from the fuelproperty sensor 45, temperature sensor 46, air-fuel ratio sensor 47, andother sensors.

The output port 37 of the electronic control unit 31 is connectedthrough corresponding drive circuits 39 to each fuel injector 11 andspark plug 10. The electronic control unit 31 in the present embodimentis formed so as to control fuel injection and control ignition. That is,the timing of injection of fuel and the amount of injection of fuel arecontrolled by the electronic control unit 31. Further the ignitiontiming of each spark plug 10 is controlled by the electronic controlunit 31. Further, the output port 37 is connected through thecorresponding drive circuits 39 to the step motor 17 for driving thethrottle valve 18, the fuel pump 29, and the EGR control valve 27. Thesedevices are controlled by the electronic control unit 31.

FIG. 2 shows an enlarged schematic cross-sectional view of a firstcombustion pressure control device in the present embodiment. Theinternal combustion engine in the present embodiment is provided with acombustion pressure control device which controls the pressure of thecombustion chamber when fuel is burned. The combustion pressure controldevice in the present embodiment is arranged in a region at the insideof the passage which communicates with the combustion chamber where theon-off valve is arranged. The combustion pressure control device in thepresent embodiment is arranged in a region at the inside of the exhaustport 9 where the exhaust valve 8 is arranged.

The first combustion pressure control device in the present embodimentis provided with a frame member 60 which is arranged at the part of theexhaust port 9 which is connected to the combustion chamber 5. The framemember 60 in the present embodiment is formed into a cylinder. The framemember 60 is fastened to a support structure constituted by the cylinderhead 4. The frame member 60 has an opening part 60 a which forms theengine exhaust passage. The frame member 60 has an engaging part 60 b.The engaging part 60 b is arranged at an end part of the frame member 60at the side which faces the combustion chamber. The engaging part 60 bis formed so as to stick out to the inside of the frame member 60.

The first combustion pressure control device in the present embodimentis provided with an interposed member which is interposed between atapered plug part 55 a of the exhaust valve 8 and a later explainedspring device. The interposed member in the present embodiment includesa tube-shaped member 61 which is formed into a tube shape. Thetube-shaped member 61 is arranged at the inside of the frame member 60.The tube-shaped member 61 is formed to be able to slide with respect tothe frame member 60. The tube-shaped member 61, as shown by the arrow201, is formed to be able to move substantially parallel to thedirection of movement of the exhaust valve 8. The end face oftube-shaped member 61 abuts against an engaging part 60 b of the framemember 60, whereby the tube-shaped member 61 is prevented from beingpulled out from the frame member 60.

The tube-shaped member 61 is open at one end part which faces thecombustion chamber 5. Further, the tube-shaped member 61 has an openingpart 61 a at its side surface. The space at the inside of thetube-shaped member 61, the opening part 61 a and the opening part 60 aof the frame member 60 configure the engine exhaust passage. The exhaustgas is discharged through the space at the inside of the tube-shapedmember 61 and the opening part 61 a. At the outer circumferentialsurface of the tube-shaped member 61, a sealing member constituted by aseal ring 69 is arranged. The seal ring 69 is arranged along thecircumferential direction of the tube-shaped member 61. The seal ring 69keeps the gas of the combustion chamber 5 from passing through theclearance between the frame member 60 and the tube-shaped member 61 andleaking to the engine exhaust passage.

One end part of the tube-shaped member 61 engages with the tapered plugpart 55 a of the exhaust valve 8. The tube-shaped member 61 includes avalve seat 62 which is arranged at the part which contacts the taperedplug part 55 a. The valve seat 62 keeps the gas of the combustionchamber 5 from leaking from the contact parts of the tapered plug part55 a and tube-shaped member 61. The tube-shaped member 61 has anabutting part 61 b at the other end part at the side opposite to theopen end part. The abutting part 61 b abuts against the later explainedfluid spring 63. In this way, the tube-shaped member 61 engages with thetapered plug part 55 a at one end part and abuts against the fluidspring 63 at the other end part.

The tube-shaped member 61 is preferably formed from a material of alarge strength and a small density so as to move in a directionsubstantially parallel to the direction of movement of the on-off valveas explained later. For example, it is preferably formed by titanium oraluminum. Due to this configuration, it is possible to maintain thestrength while improving the response of the combustion pressure controldevice.

The combustion pressure control device in the present embodiment isprovided with a spring device constituted by a fluid spring 63. Thefluid spring 63 has elasticity by sealing a compressible fluid insideit. The fluid spring 63 of the present embodiment has air sealed insidethe fluid sealing member. The fluid spring 63 in the present embodimentis formed into a ring shape. The fluid spring 63 is formed so as tosurround a guide member 53. The fluid spring 63 in the presentembodiment has a bellows part 63 a and expands or contracts in thedirection which is shown by the arrow 201 due to deformation of thebellows part 63 a.

The fluid spring 63 is arranged between the tube-shaped member 61 andthe cylinder head 4. The fluid spring 63 abuts against the cylinder head4 at one end part. The fluid spring 63 abuts against the abutting part61 b of the tube-shaped member 61 at the other end part. The fluidspring 63 biases the tube-shaped member 61 to the side which faces thecombustion chamber 5.

The exhaust valve 8 in the present embodiment is supported by the guidemember 53. The guide member 53 in the present embodiment is formed to atube shape. The guide member 53 is fastened to the cylinder head 4. Theexhaust valve 8 is formed so as to slide through the inside of the guidemember 53.

The exhaust valve 8 includes a tapered plug part 55 a with asubstantially circular shape when viewed by a plan view and ashaft-shaped part which is connected to the tapered plug part 55 a. Theshaft-shaped part in the present embodiment includes a first valve shaftpart constituted by a first stem 55 b which is connected to the taperedplug part 55 a and a second valve shaft part at the side where the camis arranged constituted by a second stem 55 c. The first stem 55 b andthe second stem 55 c are supported by the guide member 53.

At the front end part of the second stem 55 c of the exhaust valve 8, aspring retainer 52 is fastened as a fastening member. Between the springretainer 52 and the cylinder head 4, as a valve biasing member whichbiases the exhaust valve 8 in a direction by which the exhaust valve 8closes, a valve spring 51 is arranged. The valve spring 51 biases thespring retainer 52 in a direction away from the combustion chamber 5.The front end part of the second stem 55 c is pushed against the rockerarm 99. The rocker arm 99 is pushed by the exhaust cam. The internalcombustion engine in the present embodiment uses the exhaust cam to pushthe rocker arm 99. Due to the rocker arm 99, the second stem 55 c ispushed and the exhaust valve 8 opens.

The first stem 55 b and the second stem 55 c of the exhaust valve 8 areconnected through an elastic member constituted by a coil spring 54. Inthe present embodiment, inside of the second stem 55 c, a cavity part isformed. In this cavity part, the front end part of the first stem 55 bis inserted. At the inside of the cavity part of the second stem 55 c,the coil spring 54 is arranged. The coil spring 54 biases the first stem55 b and the second stem 55 c in a direction by which the first stem 55b and the second stem 55 c separate from each other.

The coil spring 54 is formed to have an elastic force of at least astrength so that when opening the exhaust valve 8 so as to open theengine exhaust passage which communicates with the combustion chamber 5,the first stem 55 b and tapered plug part 55 a move by being pushed bythe second stem 55 c. That is, the coil spring 54 is formed so that whenthe second stem 55 c of the exhaust valve 8 is pushed by the exhaust camor the rocker arm etc., the tapered plug part 55 a moves toward theinside of the combustion chamber 5. Further, the coil spring 54 isformed so as to have an elastic force by which it is pushed by the firststem 55 b and contracts corresponding to the amount of contraction ofthe fluid spring 63 when the fluid spring 63 contracts.

FIG. 3 shows another schematic cross-sectional view of the firstcombustion pressure control device in the present embodiment. FIG. 3 isa schematic cross-sectional view when cutting the part in FIG. 2 wherethe first stem and the second stem mate by another angle.

The exhaust valve 8 in the present embodiment has a stopper mechanismwhich prevents the first stem 55 b from detaching from the second stem55 c. The stopper mechanism has a stopper part 56 which is formed at thefirst stem 55 b. The stopper part 56 in the present embodiment is formedin a shaft shape. The stopper part 56 sticks out from the main body ofthe first stem 55 b toward the outside. The stopper mechanism has acutaway part 59 which is formed at the second stem 55 c. The cutawaypart 59 is formed in a direction of extension of the shaft-shaped partof the exhaust valve 8. The stopper part 56 is arranged at the inside ofthe cutaway part 59. The stopper part 56 is formed so as to enablemovement inside of the cutaway part 59. By the stopper part 56 abuttingagainst one end face of the cutaway part 59, the first stem 55 b isprevented from detaching from the second stem 55 c. Further, by the coilspring 54 expanding and contracting, the first stem 55 b moves relativeto the second stem 55 c in the direction which is shown by the arrow201. The stopper mechanism is not limited to this. Any mechanism whichprevents the first stem from being detached from the second stem may beemployed.

Referring to FIG. 2, when the pressure of the combustion chamber 5 isless than the control pressure, the tube-shaped member 61 engages withthe engaging part 60 b of the frame member 60 at the open end part dueto the pressure of the fluid inside of the fluid spring 63. The taperedplug part 55 a and the end face of the tube-shaped member 61 receive thepressure of the combustion chamber 5. In the compression stroke to theexpansion stroke of the combustion cycle, when the pressure of thecombustion chamber 5 becomes a predetermined control pressure or more,the fluid spring 63 contracts. That is, when the pushing force due tothe pressure of the combustion chamber 5 becomes larger than thereaction force of the fluid spring 63, the fluid spring 63 contracts.

FIG. 4 shows a schematic cross-sectional view when the fluid springcontracts in the first combustion pressure control device of the presentembodiment. Due to the fluid spring 63 contracting, the tube-shapedmember 61, tapered plug part 55 a, and first stem 55 b move to theoutside of the combustion chamber 5. In the present embodiment, thefirst stem 55 b of the exhaust valve 8 pushes the coil spring 54. Thecoil spring 54 contracts whereby the first stem 55 b moves relative tothe second stem 55 c. The tube-shaped member 61, tapered plug part 55 a,and first stem 55 b move to the opposite side from the side which facesthe combustion chamber 5, whereby the volume of the combustion chamber 5increases. For this reason, the pressure rise of the combustion chamber5 can be suppressed.

When the combustion of the fuel in the combustion chamber 5 progressesand the pushing force due to the pressure of the combustion chamber 5becomes smaller than the reaction force of the fluid spring 63, thefluid spring 63 expands. The tube-shaped member 61, tapered plug part 55a, and first stem 55 b move toward the inside of the combustion chamber5 and return to their original positions. Further, the volume of thecombustion chamber 5 returns to its original magnitude.

In this way, in the combustion pressure control device in the presentembodiment, when the pressure of the combustion chamber reaches thecontrol pressure, the spring device expands and contracts. The springdevice is formed so that the volume of the combustion chamber changesusing the change of the pressure of the combustion chamber as a drivesource. The control pressure in the present invention is the pressure ofthe combustion chamber when the spring device starts to change. At theinside of the fluid spring 63, a fluid of a pressure corresponding tothe control pressure is sealed. The combustion pressure control devicein the present embodiment determines the control pressure so that thepressure of the combustion chamber 5 does not become a pressure by whichabnormal combustion occurs or more.

The abnormal combustion in the present invention, for example, includescombustion other than the state when an ignition device ignites theair-fuel mixture and the combustion successively propagates from theignition point. Abnormal combustion includes, for example, the knockingphenomenon, detonation phenomenon, and preignition phenomenon. Theknocking phenomenon includes the spark knock phenomenon. The spark knockphenomenon is the phenomenon where fuel is ignited in a spark device,the flame spreads centered from the ignition device, and the air-fuelmixture including unburned fuel at the position furthest from theignition device self ignites. The air-fuel mixture at the positionfurthest from the ignition device is compressed by the combustion gasnear the ignition device, becomes high temperature and high pressure,and self ignites. When the air-fuel mixture self ignites, a shock waveis generated.

The detonation phenomenon is the phenomenon where the air-fuel mixtureignites due to a shock wave passing through the high temperature andhigh pressure air-fuel mixture. This shock wave is, for example,generated due to the spark knock phenomenon.

The preignition phenomenon is also called the “early ignitionphenomenon”. The preignition phenomenon is the phenomenon of metal atthe tip of a spark plug or carbon sludge etc. deposited inside acombustion chamber being heated to a predetermined temperature or moreand, in the state maintaining that, this part becoming the spark forignition and burning of fuel before the ignition timing.

FIG. 5 shows a graph of the pressure of the combustion chamber in aninternal combustion engine of the present embodiment. The abscissaindicates the crank angle, while the ordinate indicates the pressure ofthe combustion chamber and the amount of contraction of the fluidspring. FIG. 5 shows a graph of the compression stroke and the expansionstroke in the combustion cycle. The amount of contraction of the fluidspring 63 has a value of zero when one end part of the tube-shapedmember 61 abuts against the engaging part 60 b of the frame member 60.

Referring to FIG. 1, FIG. 2, FIG. 4, and FIG. 5, in the compressionstroke, the piston 3 rises whereby the pressure of the combustionchamber 5 rises. Here, the fluid spring 63 has a fluid of a pressurecorresponding to the control pressure sealed inside of it, so until thepressure of the combustion chamber 5 becomes the control pressure, theamount of contraction of the fluid spring 63 is zero. In the examplewhich is shown in FIG. 5, the air-fuel mixture is ignited slightly aftera crank angle of 0° (TDC). Due to the ignition, the pressure of thecombustion chamber 5 rapidly rises. When the pressure of the combustionchamber 5 reaches the control pressure, the fluid spring 63 starts tocontract. The tapered plug part 55 a, the first stem 55 b, and thetube-shaped member 61 of the exhaust valve 8 start to move relative tothe frame member 60. When the combustion of the air-fuel mixtureprogresses, the amount of contraction of the fluid spring 63 becomeslarger. For this reason, the rise in the pressure of the combustionchamber 5 is suppressed. In the example which is shown in FIG. 5, thepressure of the combustion chamber 5 is held substantially constant.

In the combustion chamber 5, when the combustion of fuel furtherprogresses, the amount of contraction of the fluid spring 63 reaches themaximum, then becomes smaller. The pressure at the inside of the fluidspring 63 is reduced toward the original pressure and the amount ofcontraction of the fluid spring 63 returns to zero.

When the pressure of the combustion chamber 5 becomes less than thecontrol pressure, the crank angle advances and the pressure of thecombustion chamber 5 is decreased.

In this way, the combustion pressure control device in the presentembodiment suppresses the rise in the pressure of the combustion chamberwhen the pressure of the combustion chamber 5 reaches the controlpressure and controls the pressure of the combustion chamber so as notto become equal to or more than the pressure where abnormal combustionoccurs.

FIG. 6 is a graph which explains the relationship between the ignitiontiming and the output torque in an internal combustion engine of acomparative example in the present embodiment. The internal combustionengine of the comparative example does not have the combustion pressurecontrol device in the present embodiment. That is, the internalcombustion engine of the comparative example does not have the fluidspring 63 and tube-shaped member 61 etc. in the present embodiment. Theexhaust valve stops from the compression stroke to the expansion stroke.Further, the shaft-shaped part of the exhaust valve 8 is formedintegrally. The graph of FIG. 6 is a graph when the internal combustionengine of the comparative example is being operated under apredetermined state. The abscissa indicates the crank angle (ignitiontiming) at the time of ignition.

It is learned that the performance of an internal combustion enginechanges depending on the timing of ignition of the air-fuel mixture. Aninternal combustion engine has an ignition timing (θmax) where theoutput torque becomes maximum. The ignition timing where the outputtorque becomes maximum changes depending on the engine speed, throttleopening degree, air-fuel ratio, compression ratio, etc. By ignition atthe ignition timing where the output torque becomes maximum, thepressure of the combustion chamber becomes higher and the heatefficiency becomes the best. Further, the output torque becomes largerand the amount of fuel consumption can be reduced. Further, the carbondioxide which is exhausted can be decreased.

In this regard, if making the ignition timing earlier, the knockingphenomenon and other abnormal combustion occurs. In particular, ifbecoming a high load, the region where abnormal combustion occursbecomes larger. In the internal combustion engine of the comparativeexample, to avoid abnormal combustion, ignition is performed retardedfrom the ignition timing (θmax) where the output torque becomes maximum.In this way, an ignition timing avoiding the region where abnormalcombustion occurs is selected.

FIG. 7 shows a graph of the pressure of the combustion chamber of theinternal combustion engine of the comparative example. The solid lineshows the pressure of the combustion chamber when stopping the feed offuel (fuel cut) and the opening degree of the throttle valve is wideopen (WOT). The pressure of the combustion chamber at this time becomesmaximum when the crank angle is 0°, that is, at compression top deadcenter. This pressure becomes the maximum pressure of the combustionchamber when not feeding fuel.

In an internal combustion engine, the pressure of the combustion chamberfluctuates depending on the ignition timing. The graph which is shown bythe broken line is a graph of ignition at the ignition timing where theoutput torque becomes maximum. The broken line shows the case ofassuming abnormal combustion does not occur. In the example which isshown in FIG. 7, the air-fuel mixture is ignited at a timing of thecrank angle slightly after 0° (TDC). In the case of ignition at theignition timing where the output torque becomes maximum, the pressure ofthe combustion chamber becomes higher. However, in an actual internalcombustion engine, the maximum pressure of the combustion chamber (Pmax)becomes larger than the pressure at which abnormal combustion occurs, sothe ignition timing is retarded. The one-dot chain line is a graph whenretarding the ignition timing. When retarding the ignition timing, themaximum pressure of the combustion chamber becomes smaller than the caseof ignition at the ignition timing where the output torque becomesmaximum.

Referring to FIG. 5, the broken line shows the graph of the case ofignition at the ignition timing (θmax) where the output torque becomesmaximum in the internal combustion engine of the comparative example. Asexplained above, in the case of ignition at this ignition timing,abnormal combustion occurs.

As opposed to this, the internal combustion engine in the presentembodiment can burn fuel so that the maximum pressure of the combustionchamber becomes less than the pressure of occurrence of abnormalcombustion. Even if advancing the ignition timing, the occurrence ofabnormal combustion can be suppressed. In particular, even in an enginewith a high compression ratio, abnormal combustion can be suppressed.For this reason, compared with the internal combustion engine of thecomparative example which retards the ignition timing shown in FIG. 7,the heat efficiency is improved and the output torque can be increased.Alternatively, the amount of fuel consumption can be reduced.

Referring to FIG. 5, in the internal combustion engine of the presentembodiment, ignition is performed at the ignition timing giving the bestheat efficiency. The internal combustion engine of the presentembodiment also enables ignition at the ignition timing where the outputtorque becomes maximum of the internal combustion engine of thecomparative example. However, the internal combustion engine in thepresent embodiment advances the ignition timing over the ignition timingwhere the output torque becomes maximum of the internal combustionengine of the comparative example. Due to this configuration, it ispossible to further improve the heat efficiency and further increase theoutput torque. In this way, the internal combustion engine in thepresent embodiment avoids abnormal combustion while enabling ignition atthe timing when the heat efficiency becomes the best.

In the present embodiment, the sealing pressure of the fluid inside ofthe fluid spring 63 becomes higher than the control pressure. Thecontrol pressure can be made larger than the maximum pressure of thecombustion chamber when stopping the feed of fuel. That is, it ispossible to set it larger than the maximum pressure of the combustionchamber of the graph of the solid line which is shown in FIG. 7.Further, the control pressure can be set to less than the pressure atwhich abnormal combustion occurs.

In the internal combustion engine of the comparative example, to retardthe ignition timing, the temperature of the exhaust gas becomes higher.Alternatively, the heat efficiency is low, so the temperature of theexhaust gas becomes higher. In the internal combustion engine of thecomparative example, to lower the temperature of the exhaust gas,sometimes the air-fuel ratio at the time of combustion is made smallerthan the stoichiometric air-fuel ratio. In this regard, the exhaustpurification device constituted by the three-way catalyst exhibits ahigh purification ability when the air-fuel ratio of the exhaust gas isnear the stoichiometric air-fuel ratio. The three-way catalyst ends upbecoming extremely small in purification performance if off from thestoichiometric air-fuel ratio. For this reason, if making the air-fuelratio at the time of combustion smaller than the stoichiometric air-fuelratio, the exhaust gas purification ability ends up falling and theunburned fuel etc. which are contained in the exhaust gas end upbecoming greater. Further, in the internal combustion engine of thecomparative example, the temperature of the exhaust gas becomes higher,so sometimes heat resistance of the exhaust purification device isdemanded and high quality materials become required or a device forcooling the exhaust gas or new structure for cooling the exhaust gasbecomes necessary.

As opposed to this, in the internal combustion engine in the presentembodiment, the heat efficiency is high, so the temperature of theexhaust gas can be kept from becoming high. In the internal combustionengine in the present embodiment, there is little need for reducing theair-fuel ratio at the time of combustion so as to lower the temperatureof the exhaust gas. When the exhaust purification device includes athree-way catalyst, the purification performance can be maintained.Furthermore, the temperature of the exhaust gas can be kept frombecoming higher, so there is less of a demand for heat resistance of themembers of the exhaust purification device. Alternatively, it ispossible to form the system even without newly adding a device forcooling the exhaust gas etc.

Further, referring to FIG. 5, in general, when raising the compressionratio of the internal combustion engine to improve the heat efficiency,the maximum pressure Pmax of the combustion chamber becomes larger. Forthis reason, it is necessary to increase the strength of the memberswhich form the internal combustion engine. However, in the internalcombustion engine in the present embodiment, the maximum pressure of thecombustion chamber can be kept from becoming greater and the componentscan be kept from become larger. For example, the diameter of theconnecting rod can be kept from becoming larger. Further, the frictionbetween components can be kept from being larger and deterioration ofthe fuel efficiency can be suppressed.

Furthermore, there is the problem that when the maximum pressure of thecombustion chamber is high, increasing the diameter of the combustionchamber is difficult. If the diameter of the combustion chamber becomeslarger, it becomes necessary to increase the strength of the supportparts of the piston and other components. However, in the presentembodiment, since it is possible to maintain the maximum pressure of thecombustion chamber low, it is possible to keep the demanded strength ofthe components low. For this reason, the diameter of the combustionchamber can easily be increased.

Next, the control pressure in the combustion pressure control device ofthe internal combustion engine of the present embodiment will beexplained.

FIG. 8 is a graph which shows the relationship between the load in aninternal combustion engine of a comparative example and the maximumpressure in the combustion chamber. The load of an internal combustionengine corresponds to the amount of injection of fuel in the combustionchamber. When abnormal combustion does not occur, as shown by the brokenline, as the load increases, the maximum pressure of the combustionchamber increases. If becoming larger than a predetermined load,abnormal combustion occurs. It is learned that the maximum pressure ofthe combustion chamber when abnormal combustion occurs is substantiallyconstant without regard as to the load.

In the internal combustion engine of the present embodiment, the controlpressure is set so that the pressure of the combustion chamber does notreach a pressure at which abnormal combustion occurs. As the controlpressure, a large pressure in the range where the maximum pressure ofthe combustion chamber at the time of combustion of the fuel becomessmaller than the pressure where abnormal combustion occurs ispreferable. The control pressure is preferably raised to near thepressure at which abnormal combustion occurs. By this configuration, theabnormal combustion can be suppressed while the heat efficiency isincreased.

FIG. 9 shows another graph of the pressure of the combustion chamber ofthe internal combustion engine in the present embodiment. FIG. 9 is anenlarged view of the part where the pressure of the combustion chamberreaches the control pressure. Referring to FIG. 4 and FIG. 9, in theinternal combustion engine of the present embodiment, when the pressureof the combustion chamber reaches the control pressure, the tube-shapedmember 61, tapered plug part 55 a, and first stem 55 b move relative tothe frame member 60. At this time, sometimes the fluid spring 63contracts and the pressure at the inside of the fluid spring 63 rises.For this reason, sometimes the pressure of the combustion chamber 5rises along with the rise of pressure at the inside of the fluid spring63. The graph of the pressure of the combustion chamber 5 becomes ashape projecting upward. When setting the control pressure, it ispreferable to set it low in anticipation of the amount of rise of thepressure inside the fluid spring 63 so that the maximum pressure of thecombustion chamber 5 does not reach the pressure where abnormalcombustion occurs.

Next, the ignition timing of the internal combustion engine of thepresent embodiment will be explained.

FIG. 10 is a graph of the pressure of the combustion chamber in internalcombustion engines of the present embodiment and the comparativeexample. The solid line shows a graph of ignition at the timing when theoutput torque becomes maximum in the internal combustion engine of thepresent embodiment. The one-dot chain line shows a graph of the case ofregarding the ignition timing in the internal combustion engine of thecomparative example.

The internal combustion engine in the present embodiment, as explainedabove, preferably selects the ignition timing θmax where the heatefficiency of the internal combustion engine becomes maximum. However,the pressure of the combustion chamber at this ignition timing becomeshigher. For example, the pressure of the combustion chamber at theignition timing of the present embodiment becomes larger than thepressure of the combustion chamber at the ignition timing of thecomparative example. For this reason, depending on the internalcombustion engine, sometimes sparks do not fly and misfire ends upoccurring. In particular, in the internal combustion engine of thepresent embodiment, ignition is performed at a crank angle near 0°(TDC). At a crank angle near 0°, the pressure of the combustion chamberis high, so sparks have difficulty flying. That is, the air density ishigh, so electrodischarge does not easily occur.

Referring to FIG. 1, if misfire occurs in the combustion chamber 5, theunburned fuel passes through the engine exhaust passage and flows intothe exhaust purification device. In the present embodiment, the unburnedfuel passes through the exhaust port 9 and flows into the three-waycatalyst 20. In this case, sometimes the unburned fuel which flows intothe three-way catalyst 20 becomes greater and the properties of theexhaust gas which is discharged into the atmosphere deteriorate.Alternatively, at the three-way catalyst 20, sometimes the unburned fuelburns and the three-way catalyst 20 becomes excessively hot.

Referring to FIG. 10, in an internal combustion engine which issusceptible to such misfire, the ignition timing can be advanced. Thatis, the ignition timing can be made earlier. For example, the ignitiontiming can be made to further advance over the ignition timing where theoutput torque becomes maximum. By making the ignition timing earlier,ignition is possible when the pressure of the combustion chamber is lowand misfires can be suppressed.

Referring to FIG. 2, the combustion pressure control device in thepresent embodiment arranges a tube-shaped member which can move in thedirection of movement of the on-off valve inside of the passage whichcommunicates with the combustion chamber. That is, part of thecombustion pressure control device can be arranged in the engine intakepassage or the engine exhaust passage. For this reason, the volume ofthe combustion chamber can be kept from becoming smaller or the diameterof the tapered plug part of the intake valve or the exhaust valve can bekept from being made smaller while the combustion pressure controldevice can be connected to the combustion chamber.

Further, the combustion pressure control device in the presentembodiment comprises the tapered plug part of the on-off valve,tube-shaped member, or other moving members which are adjacent to thecombustion chamber. These moving members are directly subjected to thepressure of the combustion chamber. Furthermore, the moving membersinclude the tapered plug part, so the area of the parts of the movingmembers which contact the combustion chamber becomes larger. For thisreason, the amount of movement of the tube-shaped member and othermoving members can be made smaller. It is therefore possible to providethe combustion pressure control device with an excellent response.

In the present embodiment, the coil spring 54 which is interposedbetween the first stem 55 b and the second stem 55 c is formed so as tocontract corresponding to the amount of contraction of the fluid spring63 when the fluid spring 63 contracts. In this regard, if the coilspring 54 becomes too small in elastic force, when opening the exhaustvalve 8, sometimes the inertia of the tapered plug part 55 a and thefirst stem 55 b will cause a delay in the timing when the tapered plugpart 55 a starts to move. For this reason, the coil spring 54 preferablyhas a large elastic force so that the movement of the tapered plug part55 a does not become delayed when opening the on-off valve. The coilspring 54 preferably has an elastic force whereby the tapered plug part55 a and the first stem 55 b start to move simultaneously with thesecond stem 55 c. The coil spring 54 preferably has an elastic forcewhereby it does not contract when opening the on-off valve. By adoptingthis configuration, it is possible to avoid delayed operation of theon-off valve.

FIG. 11 shows an enlarged schematic cross-sectional view of the secondcombustion pressure control device in the present embodiment. FIG. 11 isan enlarged schematic cross-sectional view of a mating part of the firststem and the second stem of the exhaust valve. In the second combustionpressure control device in the present embodiment, the first stem 55 band the second stem 55 c are connected through a damper 57. The damper57 in the present embodiment is arranged at the inside of the coilspring 54.

The damper 57 in the present embodiment includes a container 57 a. Thecontainer 57 a is fastened to the first stem 55 b. At the inside of thecontainer 57 a, a fluid is sealed. In the present embodiment, the insideof the container 57 a is filled with oil. The damper 57 has a platemember 57 b which is formed to be able to move at the inside of thecontainer 57 a. The plate member 57 b is formed so that oil passesaround it. The damper 57 has a supporting member 57 c which is fastenedto the second stem 55 c. The supporting member 57 c is formed into ashaft shape. The supporting member 57 c supports the plate member 57 b.

By arranging the damper 57 between the first stem 55 b and the secondstem 55 c, resonance of the exhaust valve 8 can be suppressed. When thenatural frequencies of the tapered plug part 55 a, the first stem 55 b,and the coil spring 54 match the frequency of vibration which occursdepending on the speed of internal combustion engine and resonanceoccurs, the amplitude of the vibration can be made smaller. Further,along with the opening and closing operation of the exhaust valve,sometimes the first stem 55 b ends up vibrating with respect to thesecond stem 55 c. The damper 57 can reduce the amplitude of suchvibration.

The damper in the present embodiment is an oil damper, but the inventionis not limited to this. Any damper which suppresses vibration of thefirst stem, tapered plug part, coil spring, etc. may be interposedbetween the first stem and the second stem.

FIG. 12 shows a schematic cross-sectional view of a third combustionpressure control device in the present embodiment. In the thirdcombustion pressure control device, the fluid spring 63 is arranged atthe outside of the valve spring 51 as the valve biasing member. Thefluid spring 63 is formed in a ring shape. The fluid spring 63 is formedso as to surround the valve spring 51.

The frame member 60 of the third combustion pressure control device isfastened to the cylinder head 4. The frame member 60 extends to the sideof the valve spring 51. The frame member 60 has a support part 60 c forsupporting an end part of the fluid spring 63. The frame member 60 has asupport part 60 d for supporting an end part of the valve spring 51. Theguide member 53 which supports the first stem 55 b and the second stem55 c are fastened to the support part 60 d of the frame member 60. Thetube-shaped member 61 of the third combustion pressure control devicehas an abutting part 61 b which abuts against the fluid spring 63.

FIG. 13 shows a schematic cross-sectional view of a fourth combustionpressure control device in the present embodiment. In the fourthcombustion pressure control device, the fluid spring 63 is arranged atthe inside of the valve spring 51. The fluid spring 63 is formed at thering shape. The valve spring 51 is formed so as to surround the fluidspring 63.

The frame member 60 of the fourth combustion pressure control device isfastened to the cylinder head 4. The frame member 60 extends at theinside of the valve spring 51. The frame member 60 has a support part 60c for supporting an end part of the fluid spring 63. The guide member 53is fastened to a front end of the support part 60 c. The tube-shapedmember 61 of the fourth combustion pressure control device has anabutting part 61 b which abuts against the fluid spring 63.

In the third combustion pressure control device, the fluid spring 63 isarranged at the outside of the valve spring 51, while in the fourthcombustion pressure control device, the fluid spring 63 is arranged atthe inside of the valve spring 51. That is, the fluid spring 63 and thevalve spring 51 are formed in ring shapes and are arranged in a doublestructure. By adopting this configuration, it is possible to increasethe length of the fluid spring 63 in the direction of movement of theexhaust valve 8. It is possible to increase the amount of contraction ofthe fluid spring 63 and increase the length of movement when thetube-shaped member 61, tapered plug part 55 a, and first stem 55 b move.

Further, it is possible to enlarge the opening part 61 a of thetube-shaped member 61 and the opening part 60 a of the frame member 60.For example, it is possible to make the lengths of the opening parts 60a and 61 a in the movement direction of the on-off valves longer thanthe first combustion pressure control device in the present embodiment.It is possible to make the flow sectional area of the passage whichcommunicates with the combustion chamber larger and possible to reducethe pressure loss. For example, the intake loss and exhaust loss etc.,called “the pumping loss”, can be made smaller.

When arranging the third combustion pressure control device or thefourth combustion pressure control device in the present embodiment atthe exhaust valve side, the fluid spring 63 can be arranged at theoutside of the engine exhaust passage. For this reason, it is possibleto keep the heat of the exhaust gas from causing a rise in temperatureof the fluid at the inside of the fluid spring 63. It is possible tokeep the sealing pressure at the inside of the fluid spring 63 fromchanging. As a result, it is possible to keep the control pressure fromchanging.

In the third combustion pressure control device or the fourth combustionpressure control device in the present embodiment, the end part of thefluid spring 63 and the end part of the valve spring 51 are supported bythe frame member 60, but the invention is not limited to this. They mayalso be supported by a support structure constituted by the cylinderhead 4.

The combustion pressure control device which is explained in the presentembodiment is arranged in the region where the exhaust valve isarranged, but the invention is not limited to this. It may also bearranged in the region in which the intake valve is arranged. Forexample, it is also possible to arrange the tube-shaped member at theentry part to the combustion chamber of the intake port and to arrange afluid spring between the tube-shaped member and the cylinder head. Forthe intake valve as well, in the same way as the exhaust valve in thepresent embodiment, the shaft-shaped part may include a first stem and asecond stem and the first stem and the second stem may be connectedthrough an elastic member.

In the present embodiment, the explanation was given for a combustionpressure control device which arranges a tube-shaped member etc. for asingle valve, but when a plurality of on-off valves are arranged for asingle combustion chamber, it is possible to arrange tube-shaped membersetc. for the respective on-off valves. That is, it is possible toarrange a plurality of tube-shaped members, a plurality of fluidsprings, etc. for a single combustion chamber.

In this regard, in an internal combustion engine where a plurality ofon-off valves are arranged for a single combustion chamber and wheretube-shaped members, fluid springs, etc. are arranged for the pluralityof on-off valves, sometimes the weights of the members which move whenthe pressure of the combustion chamber reaches the control pressurediffer from each other.

For example, sometimes the diameter of the tapered plug part of theintake valve is larger than the diameter of the tapered plug part of theexhaust valve. In an internal combustion engine which is provided withsuch an intake valve and the exhaust valve, when tube-shaped members,fluid springs, etc. are provided at both the intake valve side and theexhaust valve side, sometimes the responses differ in accordance withthe total weights of the members which move when the pressure of thecombustion chamber reaches the control pressure. The moving members aremembers which change in position when the fluid spring 63 contracts and,for example, include the tube-shaped member 61, tapered plug part 55 a,and first stem 55 b. The greater the total weight of the moving members,the slower the response in movement with respect to a rise in pressureof the combustion chamber 5.

When the total weights of the moving members which are arrangedcorresponding to the on-off valves differ, the larger the total weightof the moving members, the smaller the elastic force can be set for thespring device. When the spring device includes a fluid spring 63, thelarger the total weight of the moving members, the smaller the pressurecan be made at the inside of the fluid spring 63. For example, thelarger the total weight of the tapered plug part 55 a and first stem 55b of the on-off valve and the tube-shaped member 61, the smaller thepressure can be made at the inside of the fluid spring 63. By employingthis configuration, it is possible to improve the response of thecombustion pressure control device of the heavy total weight of themoving members. When arranging a plurality of tube-shaped members, fluidsprings, etc. for a single combustion chamber, the responses of movementof the members can be made substantially the same.

For example, when the diameter of the tapered plug part of the intakevalve is larger than the diameter of the tapered plug part of theexhaust valve, the sealing pressure of the fluid spring which isarranged at the intake valve side can be made smaller than the sealingpressure of the fluid spring which is arranged at the exhaust valveside. Alternatively, depending on the type of the internal combustionengine, sometimes the total weight of the members which move at theexhaust valve side is heavier than the total weight of the members whichmove at the intake valve side. In this case, it is possible to make thesealing pressure of the fluid spring at the exhaust valve side smallerthan the sealing pressure of the fluid pressure at the intake valveside. In this way, it is possible to adjust the pressure inside of afluid spring in accordance with the total weight of the moving membersof the combustion pressure control devices which are formedcorresponding to the respective on-off valves.

The spring device in the present embodiment includes a fluid spring, butthe invention is not limited to this. The spring device may be made anydevice which can apply a biasing force which corresponds to the controlpressure to the interposed member. For example, the spring device mayalso include a mechanical spring such as a coil spring. Further, whenthe spring device includes a fluid spring, it is possible to connect apressure regulating device which regulates the pressure at the inside ofthe fluid spring to the fluid spring. By changing the pressure at theinside of the fluid spring, the control pressure can be adjusted.

The interposed member in the present embodiment includes a tube-shapedmember which is formed into a tubular shape, but the invention is notlimited to this. The interposed member may be made a member of anystructure so long as it is formed to be able to move in a directionsubstantially parallel to the direction of movement of the on-off valve,one end part engages with the tapered plug part of the on-off valve, andthe other end part abuts against the fluid spring. For example, theinterposed member may have a structure where the part which engages withthe tapered plug part of the on-off valve and the part which pushesagainst the fluid spring are coupled by a shaft-shaped member.

Embodiment 2

Referring to FIG. 14 to FIG. 25, the internal combustion engine inEmbodiment 2 will be explained. The internal combustion engine in thepresent embodiment is provided with the combustion pressure controldevice.

FIG. 14 is a schematic cross-sectional view of a first combustionpressure control device in the present embodiment. FIG. 15 is aschematic perspective view of a tube-shaped member and pipe-shapedmember of the first combustion pressure control device in the presentembodiment. The combustion pressure control device in the presentembodiment is arranged in the region where the intake valve is arranged.

Referring to FIG. 14 and FIG. 15, the combustion pressure control devicein the present embodiment is provided with a movement restricting devicewhich restricts the amount of movement of the tube-shaped member 61. Themovement restricting device in the present embodiment includes apipe-shaped member 64 as a movement restricting member. The pipe-shapedmember 64 in the present embodiment is formed in a cylindrical shape.The pipe-shaped member 64 is arranged while facing the tube-shapedmember 61. The pipe-shaped member 64 has a projecting part 64 a whichprojects out toward the tube-shaped member 61. The pipe-shaped member 64abuts against the cylinder head 4 at the end at the opposite side to theside which faces the tube-shaped member 61. The pipe-shaped member 64 isformed so as not to move to the opposite side from the side which facesthe tube-shaped member 61.

The tube-shaped member 61 in the present embodiment is formed so as toextend beyond the region where the fluid spring 63 is arranged. At theend of the tube-shaped member 61 at the opposite side to the side whichfaces the combustion chamber 5, a step part 61 c is formed. In thepresent embodiment, a two-step step part 61 c is formed. The steps ofthe step part 61 c are formed so as to correspond to the shape of theprojecting part 64 a of the pipe-shaped member 64.

Referring to FIG. 15, the movement restricting device in the presentembodiment is provided with a turning device which turns the pipe-shapedmember 64. The pipe-shaped member 64 has a rack gear 64 c which isarranged at its outer circumferential surface. The rack gear 64 c isarranged so as to extend along the circumferential direction of thepipe-shaped member 64. The movement restricting device in the presentembodiment includes a pinion gear 67 and a motor 66 for driving thepinion gear 67. The pinion gear 67 engages with the rack gear 64 c. Themotor 66 is controlled by the electronic control unit 31 (see FIG. 1).By the motor 66 being driven, the pinion gear 67 rotates. The rotatingforce of the pinion gear 67 is transmitted to the rack gear 64 c,whereby, as shown by the arrow 202, the pipe-shaped member 64 turns inthe circumferential direction.

FIG. 16 shows a schematic front view which explains the positionalrelationship between projecting part of the pipe-shaped member and thestep part of the tube-shaped member in the present embodiment. By thepressure of the combustion chamber 5 reaching the control pressure, thetube-shaped member 61 moves toward the pipe-shaped member 64. The steppart 61 c of the tube-shaped member 61 abuts against the projecting part64 a of the pipe-shaped member 64 at any of the steps. By the projectingpart 64 a abutting against the step part 61 c of the tube-shaped member61, movement of the tube-shaped member 61 is restricted.

In the example which is shown in FIG. 16, the projecting part 64 a ofthe pipe-shaped member 64 abuts against the deepest part of the steppart 61 c of the tube-shaped member 61. The tube-shaped member 61becomes maximum in amount of movement. The motor 66 may be used to turnthe pipe-shaped member 64 so as to make the projecting part 64 a abutagainst the second deepest part of the step part 61 c. The amount ofmovement of the tube-shaped member 61 can be reduced. Furthermore, byturning the pipe-shaped member 64, the projecting part 64 a can be madeto abut against the top surface of the tube-shaped member 61. The amountof movement of the tube-shaped member 61 can be minimized. The movementrestricting device in the present embodiment can restrict the amount ofmovement of the tube-shaped member in stages.

FIG. 17 shows a graph of the pressure of the combustion chamber of aninternal combustion engine which is provided with the first combustionpressure control device in the present embodiment. The solid line graphis the graph of the time when the projecting part 64 a of thepipe-shaped member 64 abuts against the deepest part (first step) of thestep part 61 c of the tube-shaped member 61. The broken line graph is agraph of the time when the projecting part 64 a abuts against the seconddeepest part (second step) of the step part 61 c. The one-dot chain linegraph is a graph of the time when the projecting part 64 a abuts againstthe top surface (third step) of the tube-shaped member 61. It is learnedthat the maximum pressures Pmax1, Pmax2, and Pmax3 of the combustionchamber gradually become larger.

In this way, in the first combustion pressure control device in thepresent embodiment, the pipe-shaped member 64 can be turned to changethe position of the projecting part 64 a and thereby change the amountof movement of the tube-shaped member 61. It is possible to change themaximum pressure which the combustion chamber reaches. When the amountof movement of the tube-shaped member 61 is large, the maximum pressurewhich the combustion chamber reaches can be kept small. Further, whenthe amount of movement of the tube-shaped member 61 is small, themaximum pressure which the combustion chamber reaches can be madelarger.

The combustion pressure control device in the present embodiment isprovided with an operating state detecting device which detects theoperating state of the internal combustion engine. The combustionpressure control device in the present embodiment uses the detectedoperating state of the internal combustion engine as the basis to selectthe maximum pressure which the combustion chamber reaches. The selectedmaximum pressure of the combustion chamber can be used as the basis tochange the amount of movement of the tube-shaped member.

Here, the operating state of the internal combustion engine for changingthe maximum pressure of the combustion chamber will be explained withreference to the example of the engine speed. Referring to FIG. 1, theoperating state detecting device includes a crank angle sensor 42 fordetecting the engine speed.

FIG. 18 shows a graph which explains the relationship between the speedand a knocking margin ignition timing of the internal combustion engineof the comparative example. The internal combustion engine of thecomparative example is an internal combustion engine which does not havethe combustion pressure control device in the present embodiment. Theknocking margin ignition timing can be expressed by the followingformula:

(Knocking margin ignition timing)=(Ignition timing at which knockingoccurs)−(Ignition timing where output torque becomes maximum)

In the knocking margin ignition timing, the smaller the value, the moreeasily abnormal combustion occurs. Depending on the different speeds ofinternal combustion engines, the susceptibility to knocking differs. Forthis reason, in the combustion pressure control device of the presentembodiment, the speed of the internal combustion engine is used as thebasis to change the maximum pressure of the combustion chamber. In aninternal combustion engine, generally, the higher the speed of theinternal combustion engine, the shorter the combustion period, so themore difficult it is for abnormal combustion to occur.

FIG. 19 shows a graph of the maximum pressure of the combustion chamberwith respect to the speed of the internal combustion engine in thecombustion pressure control device of the present embodiment. In thepresent embodiment, the higher the speed of the internal combustionengine, the higher the maximum pressure of the combustion chamber isset. Referring to FIG. 1, in the present embodiment, the maximumpressure of the combustion chamber is stored as a function of the speedof the internal combustion engine in advance in the ROM 34 of theelectronic control unit 31. The electronic control unit 31 uses a crankangle sensor 42 to detect the speed of the internal combustion engineand selects the maximum pressure of the combustion chamber in accordancewith the speed. The electronic control unit 31 controls the motor 66which turns the pipe-shaped member 64 so that the pipe-shaped member 64becomes a position corresponding to the selected maximum pressure of thecombustion chamber. In the example which is shown in FIG. 19, the higherthe speed of the internal combustion engine, the more possible it is tocontrol the amount of movement of the tube-shaped member to becomesmaller.

Further, the operating state detecting device in the present embodimentincludes a fuel property detecting device which detects a property ofthe fuel which is fed to the combustion chamber. The detected propertyof the fuel is used as the basis to change the maximum pressure of thecombustion chamber. For example, sometimes the fuel of an internalcombustion engine contains alcohol. In the present embodiment, theexplanation will be given with reference to the example of an internalcombustion engine which detects the alcohol concentration as theproperty of the fuel. The properties at the time of operation of thisinternal combustion engine depend on the alcohol concentration.

FIG. 20 is a graph which explains the relationship between theconcentration of alcohol which is contained in the fuel and theretardation correction amount in the internal combustion engine of thecomparative example. The internal combustion engine of the comparativeexample retards the ignition timing when abnormal combustion occurs. Theabscissa of FIG. 20 indicates the concentration of alcohol which iscontained in the fuel, while the ordinate indicates the retardationcorrection amount when retarding the ignition timing so that abnormalcombustion does not occur. The higher the concentration of alcohol whichis contained in the fuel, the smaller the retardation correction amount.In this way, in the internal combustion engine, the higher the alcoholconcentration, the greater the resistance to abnormal combustion. Forthis reason, in the combustion pressure control device in the presentembodiment, the concentration of alcohol which is contained in the fuelis used as the basis to change the maximum pressure of the combustionchamber.

FIG. 21 shows a graph of the maximum pressure of the combustion chamberwith respect to the concentration of alcohol which is contained in thefuel in the combustion pressure control device of the presentembodiment. The higher the concentration of alcohol, the higher themaximum pressure of the combustion chamber is set. The fuel propertydetecting device in the present embodiment includes an alcoholconcentration sensor which detects the concentration of alcohol which iscontained in the fuel. Referring to FIG. 1, the internal combustionengine in the present embodiment arranges an alcohol concentrationsensor as a fuel property sensor 45 in the fuel feed flow path. Themaximum pressure of the combustion chamber demanded is stored as afunction of the alcohol concentration in advance in the ROM 34 of theelectronic control unit 31. The electronic control unit 31 detects theconcentration of alcohol which is contained in the fuel and selects themaximum pressure of the combustion chamber in accordance with theconcentration of alcohol. The electronic control unit 31 controls themotor 66 which turns the pipe-shaped member 64 so that the pipe-shapedmember 64 becomes a position which corresponds to the selected maximumpressure of the combustion chamber. In the example which is shown inFIG. 21, control can be performed to reduce the amount of movement ofthe tube-shaped member the higher the concentration of alcohol which iscontained in the fuel.

In the combustion pressure control device of the present embodiment, themaximum pressure of the combustion chamber is controlled in threestages, but the invention is not limited to this. Any number of stagesof maximum pressure can be set. For example, the step part of thetube-shaped member can be provided with any number of steps.Alternatively, the tube-shaped member may include a slanted part wherethe height successively changes instead of the step part.

As the operating state of the internal combustion engine, in addition tothe speed of the internal combustion engine and the properties of thefuel which are supplied, the intake temperature, cooling watertemperature of the internal combustion engine, temperature of thecombustion chamber right before ignition, etc. may be illustrated. Thelower these temperatures, the higher the maximum pressure of thecombustion chamber that can be set. For example, in an internalcombustion engine, the lower the temperature of the air-fuel mixture atthe time of ignition, the greater the resistance to abnormal combustion.Furthermore, when the compression ratio of the internal combustionengine is variable, the lower the compression ratio, the lower thetemperature at the time of ignition. For this reason, the lower thecompression ratio, the higher the maximum pressure of the combustionchamber can be made.

As the properties of the fuel, in addition to the alcohol concentration,the octane value of the gasoline or other indicators which show theknocking resistance may be illustrated. For example, it is possible todetect high octane value fuel or other fuel resistant to abnormalcombustion being fed into the combustion chamber and raise the maximumpressure of the combustion chamber.

In this way, by changing the maximum pressure of the combustion chamberin accordance with the operating state of the internal combustionengine, the occurrence of abnormal combustion can be suppressed whilethe maximum pressure of the combustion chamber is made larger. It istherefore possible to suppress the occurrence of abnormal combustionwhile increasing the output torque or keeping down the amount of fuelconsumption in accordance with the operating state.

Further, the movement restricting device in the present embodiment formsa step part at the tube-shaped member and forms a projecting part at thepipe-shaped member, but the invention is not limited to this. It is alsopossible to form the step part at the pipe-shaped member and form theprojecting part at the tube-shaped member. Further, the movementrestricting device in the present embodiment includes a pipe-shapedmember which faces the end face of the tube-shaped member, but theinvention is not limited to this. Any device which restricts the amountof movement of the tube-shaped member may be employed. For example,referring to FIG. 14, a rotatable movement restricting device isarranged at the inside of the cylinder head 4 and a projecting part isarranged toward the top side of the tube-shaped member from the insideof the cylinder head 4. By making the projecting part contact the steppart, the amount of movement of the tube-shaped member can berestricted.

Referring to FIG. 14 and FIG. 15, the first combustion pressure controldevice in the present embodiment is provided with a blocking devicewhich blocks at least part of the passage which communicates with thecombustion chamber. The blocking device in the present embodiment isformed so that the smaller the flow sectional area of the passage whichcommunicates with the combustion chamber, the more the circumferentialdirection flow or axial direction flow in the combustion chamber ispromoted. The blocking device in the present embodiment includes ablocking member 64 b which is attached to the pipe-shaped member 64.Further, the blocking device in the present embodiment includes a motor66 which turns the pipe-shaped member 64.

The blocking member 64 b in the present embodiment is formed so as tomove integrally with the pipe-shaped member 64. The blocking member 64 bis formed in a plate shape. The blocking member 64 b in the presentembodiment is formed into a cross-sectional arc shape. The blockingmember 64 b is formed so as to be able to block part of the opening part61 a which is formed at the tube-shaped member 61 by rotation of thepipe-shaped member 64.

FIG. 22 shows a schematic cross-sectional view of an internal combustionengine which is provided with the first combustion pressure controldevice in the present embodiment. FIG. 22 is a schematic cross-sectionalview of a combustion chamber, engine intake passage, and engine exhaustpassage of the internal combustion engine. The combustion chamber 5 isfed a mixture of air and fuel through an engine intake passageconstituted by the intake port 7. The exhaust gas which is produced dueto combustion of the fuel in the combustion chamber 5 is dischargedthrough an engine exhaust passage constituted by the exhaust port 9.

In the present embodiment, the cylinder head 4 is formed with entryparts 7 a and 7 b of the combustion chamber 5. Further, the cylinderhead 4 is formed with exit parts 9 a and 9 b of the combustion chamber5. The internal combustion engine in the present embodiment arranges twointake valves 6 and two exhaust valves 8 for one combustion chamber 5.The numbers of intake valves and exhaust valves which are arranged atone combustion chamber 5 are not limited to this. Any numbers may beemployed.

In the example of the internal combustion engine which is shown in FIG.22, among the entry part 7 a and the entry part 7 b of the combustionchamber 5, the blocking device of the combustion pressure control deviceis arranged corresponding to the entry part 7 a. Referring to FIG. 15,by driving the motor 66, the pipe-shaped member 64 and the blockingmember 64 b rotate. By the blocking member 64 b rotating, part of theopening part 61 a of the tube-shaped member 61 is blocked. The flowsectional area of the engine intake passage becomes smaller.

Referring to FIG. 22, at the combustion chamber 5, the air-fuel mixtureflows in from the entry part 7 a as shown by the arrow 204. Further, atthe combustion chamber 5, the air-fuel mixture flows in from the entrypart 7 b as shown by the arrow 203. By the blocking member 64 b beingarranged at the intake port 7 which communicates with the entry part 7a, the flow sectional area of the engine intake passage whichcommunicates with the entry part 7 a becomes smaller. The flow rate ofthe air-fuel mixture which flows in from the entry part 7 a becomessmaller.

As opposed to this, the blocking member 64 b is not arranged at theentry part 7 b of the combustion chamber 5, so the flow rate of theair-fuel mixture which flows in from the entry part 7 b becomes largerthan the flow rate of the air-fuel mixture which flows in from the entrypart 7 a. For this reason, as shown by the arrow 203, a flow whichcircles along the circumferential direction of the combustion chamber 5is promoted. That is, a swirl flow is promoted in the combustion chamber5.

FIG. 23 shows a schematic cross-sectional view of another internalcombustion engine which is provided with the first combustion pressurecontrol device in the present embodiment. FIG. 23 is a schematiccross-sectional view of a combustion chamber, engine intake passage, andengine exhaust passage of another internal combustion engine. In anotherinternal combustion engine, first combustion pressure control devices inthe present embodiment are attached corresponding to both of the entrypart 7 a and the entry part 7 b of the combustion chamber 5. In anotherinternal combustion engine, to strengthen the swirl flow, the intakeport 7 which is communicated with the entry part 7 a is bent.

In another internal combustion engine, the blocking members 64 b of theblocking devices which are arranged at the entry part 7 a and the entrypart 7 b are used to block parts of the respective passages of theintake ports 7. The blocking member 64 b which is arranged correspondingto the entry part 7 a and the blocking member 64 b which is arrangedcorresponding to the entry part 7 b are arranged in regions near thecenter of the approximately circular shape when viewing the combustionchamber 5 from a plan view. These intake ports 7 open at regions closeto the outer circumference of the combustion chamber 5. For this reason,the air-fuel mixture which flows through the entry part 7 a into thecombustion chamber 5, as shown by the arrow 205, promotes the flow inthe circumferential direction of the combustion chamber 5. Further, theair-fuel mixture which flows through the entry part 7 b into thecombustion chamber 5, as shown by the arrow 206, promotes the flow inthe circumferential direction of the combustion chamber 5. In this way,in another internal combustion engine as well, the flow in thecircumferential direction can be promoted.

The blocking members 64 b of the first combustion pressure controldevices in the present embodiment are formed so as to block the entireopening parts 61 a in the height direction, but the invention is notlimited to this. They may also be formed so as to block parts of theopening parts 61 a in the height direction. Further, the blockingmembers 64 b may also be formed to block the entire opening parts 61 a.Further, the blocking members of the blocking devices can be made anyshapes which form a swirl flow in accordance with the angle or shape bywhich the engine intake passage is connected to the combustion chamber.

FIG. 24 is a schematic perspective view of the part of the tube-shapedmember and pipe-shaped member of a second combustion pressure controldevice in the present embodiment. In the second combustion pressurecontrol device, the pipe-shaped member 64 is provided with a blockingmember 64 b which is shorter in length in the height direction of theopening part 61 a. The second combustion pressure control devicepromotes the flow in the axial direction in the combustion chamber 5.The blocking member 64 b in the second combustion pressure controldevice is formed so as to block the top part in the opening part 61 a ofthe tube-shaped member 61. In the present embodiment, the blockingmember 64 b blocks the approximately top half of the opening part 61 a.At this time, the approximately bottom half of the opening part 61 a isopen.

FIG. 25 shows a schematic cross-sectional view of an internal combustionengine which is provided with the second combustion pressure controldevice in the present embodiment. FIG. 25 is a schematic cross-sectionalview when a blocking device is used to block part of the engine intakepassage. By using the blocking member 64 b to block the top part of theopening part 61 a of the tube-shaped member 61, the engine intakepassage is restricted to the region at the bottom of the intake port 7.The air-fuel mixture which passes through the intake port 7 and flowsinto the combustion chamber 5, as shown by the arrow 207, becomes largerin speed component in the horizontal direction. As a result, the flow inthe axial direction of the combustion chamber 5 can be promoted. Thatis, a tumble flow can be promoted in the combustion chamber 5.

The blocking member of the second combustion pressure control device inthe present embodiment is formed so as to block part of the opening part61 a in the width direction, but the invention is not limited to this.The blocking member may so be formed so as to cover the entire widthdirection of the opening part 61 a. Further, the blocking member of theblocking device may be made any shape which forms a tumble flowcorresponding to the angle or shape by which the engine intake passageis connected to the combustion chamber.

Further, the blocking device in the present embodiment is formed byattaching a blocking member to a pipe-shaped member and rotating theblocking member so that the blocking member blocks the opening part ofthe tube-shaped member, but the invention is not limited to this. Theblocking device need only be formed so as to block at least part of thepassage which communicates with the combustion chamber and therebypromote a swirl flow, tumble flow, or other agitated flow in thecombustion chamber.

In this regard, when the internal combustion engine is provided with anoperating state detecting device, it is possible to form a swirl flow,tumble flow, or other agitated flow in accordance with the detectedoperating state.

An internal combustion engine sometimes is liable to misfire in apredetermined operating state. For example, in an internal combustionengine which is provided with an exhaust gas recirculation system or aninternal combustion engine which burns fuel in a state increasing theair-fuel ratio at the time of combustion (for example, a lean burnengine), etc., misfire is sometimes liable to occur. In these internalcombustion engine which is provided with an exhaust gas recirculationsystem and internal combustion engine which controls the air-fuel ratioto become large, the intake loss and exhaust loss can be reduced and theheat efficiency is improved. That is, the pumping loss becomes smallerand the heat efficiency is improved. In this regard, in such an internalcombustion engine, the air-fuel ratio when the fuel is burning becomeslarger, so the combustion speed becomes slower. For this reason, misfireeasily occurs in the combustion chamber.

In an internal combustion engine in which misfire is liable to occur, itis possible to form a swirl flow or tumble flow or other agitated flowinside of the combustion chamber so as to increase the combustion speedand suppress misfire. On the other hand, if forming a swirl flow, tumbleflow, etc. in the combustion chamber, the combustion speed becomeslarger, so the heat efficiency becomes lower. If the combustion speed islarge, the highest temperature of the combustion gas when burned becomeshigher. For this reason, the amount of heat which is discharged from thecombustion chamber to the outside becomes larger and the heat efficiencybecomes lower.

Referring to FIG. 15 and FIG. 24, the first combustion pressure controldevice and the second combustion pressure control device in the presentembodiment are provided with a movement restricting device and blockingdevice. The combustion pressure control device in the present embodimentis formed so that the smaller the flow sectional area of the passagewhich communicates with the combustion chamber due to the blockingdevice, the smaller the amount of movement the tube-shaped member isrestricted to. That is, it is formed so that the stronger the agitatedflow in the combustion chamber is promoted, the higher the highestpressure of the combustion chamber becomes. For this reason, theagitated flow can be promoted and misfire suppressed while the heatefficiency is raised.

Referring to FIG. 1, the internal combustion engine in the presentembodiment is provided with an exhaust gas recirculation system. Theexhaust gas recirculation system includes an EGR gas supply line 26 andEGR control valve 27. The recirculation rate of the exhaust gas can beadjusted by changing the opening degree of the EGR control valve 27. Inthe present embodiment, the operating state detecting device detects therecirculation rate of the exhaust gas. The recirculation rate of theexhaust gas can be estimated based on the output value of the air flowmeter 16, the opening degree of the EGR control valve, etc.

The internal combustion engine in the present embodiment can use theblocking device to reduce the flow sectional area of the engine intakepassage to promote an agitated flow in the combustion chamber whenincreasing the recirculation rate of the exhaust gas. By promoting anagitated flow, misfires can be suppressed. Furthermore, the movementrestricting device can be used to reduce the amount of movement of thetube-shaped member so as to increase the maximum pressure which thecombustion chamber reaches. By increasing the maximum pressure which thecombustion chamber reaches, the heat efficiency can be improved.

Further, the internal combustion engine in the present embodiment canperform control so that the air-fuel ratio at the time of combustionbecomes large. In the present embodiment, the operating state detectingdevice detects the air-fuel ratio at the time of combustion. Theair-fuel ratio at the time of combustion can be estimated based on theamount of injection of fuel from the fuel injector 11, the output valueof the air flow meter 16, etc. The internal combustion engine in thepresent embodiment can use the blocking device to reduce the flowsectional area of the engine intake passage and promote an agitated flowin the combustion chamber when increasing the air-fuel ratio at the timeof combustion. By promoting an agitated flow, misfire can be prevented.Furthermore, the movement restricting device can be used to reduce theamount of movement of the tube-shaped member and increase the maximumpressure which the combustion chamber reaches. By increasing the maximumpressure which the combustion chamber reaches, the heat efficiency canbe improved.

In this way, the combustion pressure control device in the presentembodiment can promote an agitated flow which is formed in thecombustion chamber and raise the maximum pressure which is reached inthe combustion chamber.

The combustion pressure control device in the present embodiment isprovided with both the movement restricting device which restricts theamount of movement of the tube-shaped member and the blocking devicewhich blocks at least part of the passage which communicates with thecombustion chamber, but the invention is not limited to this. Thecombustion pressure control device may also be provided with just one.For example, a combustion pressure control device which does not includea blocking device, but includes a movement restricting device may alsobe arranged in the region where the exhaust valve is arranged.

The rest of the configuration, actions, and effects are similar to thoseof Embodiment 1, so the explanations will not be repeated here.

Embodiment 3

Referring to FIG. 26 to FIG. 35, an internal combustion engine inEmbodiment 3 will be explained. The internal combustion engine in thepresent embodiment is provided with a combustion pressure controldevice. In the present embodiment, the explanation will be given withreference to the example of a combustion pressure control device whichis arranged in a region where the exhaust valve is arranged.

FIG. 26 is a schematic cross-sectional view of the first combustionpressure control device in the present embodiment. At the part where theexhaust port 9 is connected to the combustion chamber 5, a frame member60, tube-shaped member 61, and fluid spring 63 are arranged in the sameway as the first combustion pressure control device in Embodiment 1 (seeFIG. 2). The first combustion pressure control device of the presentembodiment does not have a coil spring arranged between the first stem55 b and the second stem 55 c of the exhaust valve 8. The shaft-shapedpart of the exhaust valve 8 is comprised of the first stem 55 b and thesecond stem 55 c formed integrally.

FIG. 27 shows a schematic perspective view of the part of the cam andthe rocker arm which drive the exhaust valve. Referring to FIG. 26 andFIG. 27, the combustion pressure control device in the presentembodiment is provided with a cam for closing or opening the on-offvalve. The combustion pressure control device in the present embodimentis provided with an exhaust cam 90 which drives the exhaust valve 8.

The exhaust cam 90 is supported by the cam shaft 92. As shown by thearrow 209, by the cam shaft 92 rotating, the exhaust cam 90 rotates. Thecombustion pressure control device in the present embodiment is providedwith a rocker arm 93 serving as a transmission member which transmitsthe drive force of the exhaust cam 90. The rocker arm 93 is supported bya rocker shaft 94. The rocker arm 93, as shown by the arrow 208, isformed so as to swing using the rocker shaft 94 as the center ofrocking. The rocker arm 93 has a pushing part 93 a which pushes theexhaust valve 8. The pushing part 93 a is formed so as to push the endpart of the second stem 55 c of the exhaust valve 8.

The rocker arm 93 in the present embodiment has an abutting part 95which abuts against the exhaust cam 90. The abutting part 95 has aprojecting part 95 a which sticks out toward the exhaust cam 90. Theprojecting part 95 a in the present embodiment is formed so as to extendin the width direction of the exhaust cam 90.

The combustion pressure control device in the present embodiment isprovided with a variable valve mechanism which changes the phase of theexhaust cam with respect to the crank angle. That is, it is providedwith a variable valve mechanism which changes the phase of the exhaustcam with respect to the position of the piston 3 in the cylinder. In thepresent embodiment, as the variable valve mechanism, a variable valvetiming device 70 is provided. The variable valve timing device 70 isattached to an end part of the cam shaft 92. The variable valve timingdevice 70 is connected to an output port 36 of the electronic controlunit 31. The variable valve timing device 70 is controlled by theelectronic control unit 31 (see FIG. 1).

FIG. 28 shows a schematic view of a variable valve timing device in thepresent embodiment. The variable valve timing device 70 in the presentembodiment is provided with a timing pulley 71 which rotates in thedirection of the arrow 209 by a timing belt which is engaged with acrankshaft of the engine body and a cylindrical housing 72 which rotatestogether with the timing pulley 71. The variable valve timing device 70is provided with a rotary shaft 73 which rotates together with the camshaft 92 and can rotate relative to the cylindrical housing 72, aplurality of partition walls 74 which extend from an innercircumferential surface of the cylindrical housing 72 to an outercircumferential surface of the rotary shaft 73, and a vane 75 whichextends between each two partition walls 74 from the outercircumferential surface of the rotary shaft 73 to the innercircumferential surface of the cylindrical housing 72. At the two sidesof each vane 75, an advancement-use hydraulic chamber 76 and aretardation-use hydraulic chamber 77 are formed.

The variable valve timing device 70 includes a feeding device whichfeeds working oil to the hydraulic chambers 76 and 77. The feedingdevice includes a working oil feed control valve 78. The working oilfeed control valve 78 includes hydraulic ports 79 and 80 which arerespectively connected to the hydraulic chambers 76 and 77, a feed port82 of working oil which is discharged from the hydraulic pump 81, a pairof drain ports 83 and 84, and a spool valve 85 which communicates andblocks the ports 79, 80, 82, 83, and 84.

When making the phase of the exhaust cam 90 which is fastened to the camshaft 92 advance, in FIG. 28, the spool valve 85 is moved to the right.Working oil which is fed from the feed port 82 is fed through thehydraulic port 79 to the advancement-use hydraulic chamber 76 andworking oil inside of the retardation-use hydraulic chamber 77 isdischarged from the drain port 84. At this time, the rotary shaft 73 ismade to rotate relative to the cylindrical housing 72 in the directionof the arrow 209.

As opposed to this, when retarding the phase of the exhaust cam 90 whichis fastened to the cam shaft 92, in FIG. 28, the spool valve 85 is movedto the left. The working oil which is fed from the feed port 82 is fedthrough the hydraulic port 80 to the retardation-use hydraulic chamber77 and the working oil inside the advancement-use hydraulic chamber 76is discharged from the drain port 83. At this time, the rotary shaft 73is rotated relative to the cylindrical housing 72 in the directionopposite to the arrow 209.

When the rotary shaft 73 rotates relative to the cylindrical housing 72,the spool valve 85 is returned to the neutral position whereby therotating action of the rotary shaft 73 stops. The rotary shaft 73 isheld at the position at that time. Therefore, the variable valve timingdevice 70 can be used to make the phase of the exhaust cam 90 which isfastened to the cam shaft 92 advance by exactly the desired amount.Alternatively, the phase of the exhaust cam 90 can be retarded byexactly the desired amount.

In this way, by driving the variable valve timing device, the phase ofthe exhaust cam 90 relative to the crank angle can be made to changewithin a predetermined range of angle. Note that, the variable valvemechanism is not limited to the above variable valve timing device. Anydevice which can adjust the phase of the cam can be employed.

FIG. 29 shows an enlarged schematic cross-sectional view of an exhaustcam in the present embodiment. The exhaust cam 90 has a base circle part90 a which has an approximately circular shape in a cross-sectional viewand cam nose part 90 b which bulges out from the base circle part 90 ato the outside. If referring to the amount of bulge from the base circlepart 90 a in the radial direction as “the amount of cam lift L”, at thecam nose part 90 b, the amount of cam lift L becomes a positive value.Referring to FIG. 26, the cam nose part 90 b pushes against theprojecting part 95 a of the abutting part 95, whereby the rocker arm 93rocks. By the pushing part 93 a of the rocker arm 93 pushing the exhaustvalve 8, the exhaust valve 8 opens.

Referring to FIG. 29, the exhaust cam 90 in the present embodiment has arecessed part 90 c which is recessed from part of the outercircumferential surface. In the range where the recessed part 90 c isformed, the amount of cam lift L becomes a negative value. The recessedpart 90 c in the present embodiment is formed by a depth and phaseenabling the exhaust valve 8 to freely move in a direction away from thecombustion chamber 5 during the time period when the phase of theexhaust cam 90 is set to the retarded side and the pressure of thecombustion chamber 5 reaches the control pressure.

Referring to FIG. 26, if the phase of the exhaust cam 90 is set theretarded side and the pressure of the combustion chamber 5 reaches thecontrol pressure, the fluid spring 63 contracts. The exhaust valve 8moves in a direction away from the combustion chamber 5. The front endof the exhaust valve 8 lifts up the pushing part 93 a of the rocker arm93. At this time, the projecting part 95 a of the abutting part 95 isarranged at the inside of the recessed part 90 c of the exhaust cam 90.A clearance is formed between the projecting part 95 a and the bottomsurface of the recessed part 90 c. In this way, the recessed part 90 cis formed so that the on-off valve can move in accordance with theamount of contraction of the fluid spring 63 in the time period when thefluid spring 63 is contracting.

FIG. 30 shows a time chart of the combustion pressure control device inthe present embodiment. The amount of cam lift of the exhaust cam willbe explained for the case of setting the exhaust cam at a retarded sidephase and the case of setting the exhaust cam at an advanced side phase.In the example which is shown in FIG. 30, in the time period from thetiming t1 to the timing t3, the pressure of the combustion chamber isthe control pressure or more and the fluid spring 63 contracts.

When setting the phase of the exhaust cam at the retarded side, in thetime period after ignition until the pressure rises, the amount of camlift is substantially zero. Along with the rise of the pressure of thecombustion chamber, the amount of cam lift decreases. In the examplewhich is shown in FIG. 30, the amount of cam lift L of the exhaust cambecomes the minimum until the timing t1. In the time period from thetiming t1 to the timing t3, the minimum amount of cam lift ismaintained. When setting the phase of the exhaust cam at the retardedside, a clearance is formed between the projecting part 95 a of theabutting part 95 and the recessed part 90 c until the pressure of thecombustion chamber reaches the control pressure. The constraint on theexhaust valve 8 is released. The exhaust valve 8 is raised correspondingto the amount by which the fluid spring 63 contracts. For this reason,the pressure of the combustion chamber in the case of setting the phaseof the exhaust cam at the retarded side is held substantially constantin the time period when the fluid spring 63 is contracting as shown inEmbodiment 1 (for example, see FIG. 5).

The combustion pressure control device in the present embodiment isprovided with an operating state detecting device. The operating statedetecting device detects the operating state and, in a predeterminedoperating state, performs control so as to make the maximum pressure ofthe combustion chamber rise. In the combustion pressure control devicein the present embodiment, when making the maximum pressure of thecombustion chamber rise, the variable valve timing device 70 is used tomake the phase of the exhaust cam 90 advance.

By using the variable valve timing device 70 to make the phase of theexhaust cam 90 advance, as shown by the arrow 211, the timing where theamount of lift of the exhaust cam becomes negative becomes earlier. Thephase of the recessed part 90 c of the exhaust cam 90 advances. For thisreason, in the latter half of the time period when the pressure of thecombustion chamber 5 reaches the control pressure, the projecting part95 a of the abutting part 95 can be made to contact the wall surface ofthe recessed part 90 c of the exhaust cam 90. The wall surface of therecessed part 90 c of the exhaust cam 90 is used to push the abuttingpart 95. For this reason, movement of the exhaust valve 8 in a directionaway from the combustion chamber 5 is restricted. The exhaust valve 8 ispushed through the rocker arm 93. The exhaust valve 8 moves toward thecombustion chamber 5. The volume of the combustion chamber 5 becomessmaller and the pressure of the combustion chamber 5 rises.

In the example of operational control which is shown in FIG. 30, at thetiming t2, the projecting part 95 a of the abutting part 95 contacts thewall surface of the recessed part 90 c. At the timing t2, the clearancebetween the projecting part 95 a and the recessed part 90 c of theexhaust cam 90 becomes zero. In the time period from the timing t2 tothe timing t3, the exhaust valve 8 is moving toward the combustionchamber 5. The amount of contraction of the fluid spring 62 accompanyingthis movement is rapidly decreased from the case of setting the phase ofthe exhaust cam 90 at the retarded side and approaches zero. In the timeperiod from the timing t2 to the timing t3, the pressure of thecombustion chamber 5 rises.

In this way, in the combustion pressure control device of the presentembodiment, it is possible to use the variable valve timing device tochange the phase of the cam and thereby restrict the amount of movementof the exhaust valve during the time period when the fluid spring iscontracting. In the combustion pressure control device of the presentembodiment as well, in the same way as the combustion pressure controldevice in Embodiment 2, the maximum pressure of the combustion chambercan be adjusted in accordance with the operating state which is detectedby the operating state detecting device.

In the example of operational control which is shown in FIG. 30, in thetime period when the pressure of the combustion chamber reaches thecontrol pressure, the amount of movement of the exhaust valve isrestricted in the time period when the amount of contraction of thefluid spring is decreasing. By advancing the phase of the exhaust cam,the maximum pressure of the combustion chamber is made to rise, but theinvention is not limited to this. It is also possible to retard thephase of the exhaust cam to thereby bring the abutting part of therocker arm into contact with the wall surface of the recessed part ofthe exhaust cam so as to make the maximum pressure of the combustionchamber rise. That is, the amount of movement of the exhaust valve mayalso be restricted in the time period during which the amount ofcontraction of the fluid spring increases. However, by restricting theamount of movement of the exhaust valve in the time period when theamount of contraction of the fluid spring is decreasing, the frictionbetween the recessed part of the exhaust cam and the abutting part ofthe rocker arm can be reduced. Alternatively, the torque for turning theexhaust cam can be reduced.

FIG. 31 shows a schematic perspective view of the part of the exhaustcam and the rocker arm in the second combustion pressure control devicein the present embodiment. The second combustion pressure control deviceof the present embodiment is provided with the first exhaust cam 90 andthe second exhaust cam 91 for driving the exhaust valve 8 and is formedso that two exhaust cams can be switched between. The rocker arm 93 hasan abutting part 95 which abuts against the first exhaust cam 90 and anabutting part 96 which abuts against the second exhaust cam 91. Thesecond combustion pressure control device in the present embodiment isnot provided with the variable valve timing device, but the invention isnot limited to this. The variable valve timing device may also beprovided.

The first exhaust cam 90 is similar to the exhaust cam 90 of the firstcombustion pressure control device in the present embodiment (see FIG.29). The first exhaust cam 90 is formed with a recessed part 90 c. Therecessed part 90 c is formed so as not to constrain the movement of theexhaust valve 8 in the time period when the pressure of the combustionchamber 5 reaches the control pressure.

FIG. 32 shows a schematic cross-sectional view of a second exhaust camin the present embodiment. The second exhaust cam 91 in the presentembodiment has a base circle part 91 a which has an approximatelycircular shape in a cross-sectional view, cam nose part 91 b, andrecessed part 91 c. The recessed part 91 c of the second exhaust cam 91is formed shallower than the recessed part 90 c of the first exhaust cam90. The magnitude (absolute value) of the amount of negative lift L atthe bottom of the recessed part 91 c of the second exhaust cam 91 issmaller than the magnitude (absolute value) of the amount of lift L ofthe bottom of the recessed part 90 c of the first exhaust cam 90. Therecessed part 91 c is formed in the region or phase which drives theexhaust valve during the time period when the pressure of the combustionchamber reaches the control pressure. Furthermore, the recessed part 91c is formed shallow so as to constrain movement of the exhaust valve 8during the time period when the pressure of the combustion chamberreaches the control pressure.

Referring to FIG. 31, the combustion pressure control device of thepresent embodiment is provided with a switching device 97 which switchesbetween the first exhaust cam 90 and the second exhaust cam 91 as thecam for operating the exhaust valve 8. The cam switching device 97 inthe present embodiment is formed to be able to transmit the drive forceof the second exhaust cam 91 to the rocker arm 93 and disengage it. Whenthe drive force of the second exhaust cam 91 is transmitted to therocker arm 93, the transmission of the drive force of the first exhaustcam 90 is disengaged.

FIG. 33 shows a first schematic cross-sectional view of a cam switchingdevice in the present embodiment. FIG. 33 is a schematic cross-sectionalview when the transmission of drive power of the second exhaust cam 91is disengaged. The cam switching device in the present embodiment isprovided with a housing 110. Inside of the housing 110, a stopper member111 is arranged. The stopper member 111 is formed into a cross-sectionalU-shape. The stopper member 111 is formed to be able to move at theinside of the housing 110.

Inside of the stopper member 111, a spring 114 is arranged. At the frontend of the spring 114, a pushing member 112 is arranged. The spring 114biases the pushing member 112 in the pushing direction. The stoppermember 111 is pushed to the opposite side from the side facing thesupporting member 113.

The switching device in the present embodiment includes the supportingmember 113 which is fastened to the abutting part 96. The supportingmember 113 is supported by the housing 110. The supporting member 113 isformed to be able to move in the axial direction with respect to thehousing 110. The end face 111 a of the stopper member 111 abuts againstthe supporting member 113. Further, the end face of the pushing member112 also abuts against the supporting member 113. The abutting part 96is biased by the spring 115 to the side where the abutting part 96 facesthe exhaust cam 91. The abutting part 96 is biased in a direction whereit jumps out from the housing 110. The abutting part 96 and thesupporting member 113, as shown by the arrow 210, freely move in thedirection in which the supporting member 113 extends.

Referring to FIG. 31 and FIG. 33, by the second exhaust cam 91 pushingagainst the abutting part 96, the spring 115 contracts and the abuttingpart 96 is pushed down. FIG. 33 shows the state where the abutting part96 is pushed down. The drive force of the second exhaust cam 91 isabsorbed by the movement of the abutting part 96 and the supportingmember 113. The link between the second exhaust cam 91 and the rockerarm 93 is disengaged. In this case, the rocker arm 93 is driven by thefirst exhaust cam 90.

The housing 110 of the cam switching device 97 is formed with an oilpath 110 a. The oil path 110 a is formed so as to be able to feedworking oil to the space in which the stopper member 111 is arranged.The oil path 110 a is, for example, connected through the oil path whichis formed at the inside of the rocker shaft 94 to the working oilfeeding device 116. The inside of the housing 110 is fed with workingoil for pushing the stopper member 111 in the direction which is shownby the arrow 212.

FIG. 34 shows a second schematic cross-sectional view of a cam switchingdevice in the present embodiment. FIG. 34 is a schematic cross-sectionalview when the drive force of the second exhaust cam 91 is beingtransmitted. The working oil feeding device 116 is used to feed thepressurized oil which has passed through the oil line 110 a to theinside of the housing 110. Due to a pushing force of the working oillarger than the biasing force of the spring 114, the stopper member 111moves in the direction which is shown by the arrow 212. When theabutting part 96 rises, the stopper member 111 moves, whereby part ofthe stopper member 111 is arranged below the supporting member 113. Forthis reason, the abutting part 96 and the supporting member 113 arerestricted from moving in a direction away from the second exhaust cam91.

In this case, referring to FIG. 31, the drive force by the secondexhaust cam 91 is transmitted to the rocker arm 93. The first exhaustcam 90 and the second exhaust cam 91 have substantially the same shapesof the base circle parts 90 a and 91 a and cam nose parts 90 b and 91 b.In this regard, the recessed part 91 c of the second exhaust cam 91 isformed so as to restrict the amount of movement of the exhaust valve 8.The projecting part 96 a of the abutting part 96 contacts the recessedpart 91 c of the second exhaust cam 91. In the time period during whichthe pressure of the combustion chamber reaches the control pressure,movement of the exhaust valve 8 toward the outside of the combustionchamber can be restricted. The exhaust valve 8 is pushed by the secondexhaust cam 91. The amount of contraction of the fluid spring and theamount of movement of the tube-shaped member can be restricted. As aresult, the maximum pressure which the combustion chamber 5 reaches canbe raised. On the other hand, the projecting part 95 a of the abuttingpart 95 is separated from the recessed part 90 c of the first exhaustcam 90 in this state. The transmission of the drive force of the firstexhaust cam 90 is disengaged.

FIG. 35 is a graph of the pressure of the combustion chamber of thesecond combustion pressure control device in the present embodiment. Itis learned that compared to when using the first exhaust cam 90 to drivethe exhaust valve, using the second exhaust cam 91 to drive the exhaustvalve increases the maximum pressure which the combustion chamberreaches.

In the second combustion pressure control device of the presentembodiment, by switching the exhaust cam, it is possible to adjust themaximum pressure which the combustion chamber reaches. For example, theoperating state detecting device can be used to detect the operatingstate of the internal combustion engine and the maximum pressure of thecombustion chamber can be selected in accordance with the operatingstate.

The cam switching device of the second combustion pressure controldevice in the present embodiment is formed so as to transmit ordisengage the drive force of the second exhaust cam, but the inventionis not limited to this. The cam switching device can be made any devicewhich can switch among a plurality of cams. Further, in the presentembodiment, two cams are arranged, but the invention is not limited tothis. Three or more cams may also be arranged.

In the first combustion pressure control device and the secondcombustion pressure control device of the present embodiment, the driveforce of the exhaust cam is transmitted through the rocker arm to theexhaust valve, but the invention is not limited to this. It is alsopossible to configure them so that the drive force of the exhaust valveis directly transmitted to the exhaust valve without going through therocker arm.

Further, in the combustion pressure control device of the presentembodiment, the explanation was given with reference to an example inwhich an on-off valve constituted by the exhaust valve and a camconstituted by the exhaust cam are provided, but the invention is notlimited to this. It is also possible to provide an on-off valveconstituted by an intake valve and a cam constituted by an intake cam.That is, the combustion pressure control device in the presentembodiment may also be arranged in a region in which the intake valve isprovided.

The rest of the configuration, actions, and effects are similar to thoseof Embodiment 1 or 2, so the explanation will not be repeated.

Embodiment 4

Referring to FIG. 36 to FIG. 40, the internal combustion engine inEmbodiment 4 will be explained. The internal combustion engine in thepresent embodiment is provided with a combustion pressure controldevice. In the present embodiment, among the intake valve and theexhaust valve, the explanation will be given with reference to theexample of a combustion pressure control device which is attached to aregion in which the exhaust valve is provided.

FIG. 36 is a schematic cross-sectional view of the combustion pressurecontrol device in the present embodiment. The part where the exhaustport 9 is connected to the combustion chamber 5 being provided with theframe member 60, tube-shaped member 61, and fluid spring 63 is similarto the structure in the first combustion pressure control device inEmbodiment 1 (see FIG. 2). The combustion pressure control device in thepresent embodiment differs from Embodiment 1 in the drive device whichoperates the on-off valve constituted by the exhaust valve 8. Thecombustion pressure control device in the present embodiment is providedwith an electromagnetic drive device 120 for driving the exhaust valve8. The electromagnetic drive device 120 includes an electromagnet. Themagnetic force of the electromagnet can be used to open the exhaustvalve 8.

The electromagnetic drive device 120 in the present embodiment includesa housing 128. The housing 128 in the present embodiment is fastened tothe cylinder head 4. At the inside of the housing 128, the upper core121 and the lower core 122 are arranged. The upper core 121 and thelower core 122 are formed by a magnetic substance. The upper core 121and the lower core 122 are fastened to the housing 128. At the inside ofthe upper core 121, the upper coil 123 is arranged. Furthermore, at theinside of the lower core 122, the lower coil 124 is arranged. The uppercoil 123 is connected to a power feeding device 126 which feeds powerfor magnetization. The lower coil 124 is connected to a power feedingdevice 127 which feeds power for magnetization. These power feedingdevices 126 and 127 are controlled by the electronic control unit 31.

The second stem 55 c of the exhaust valve 8 passes through the uppercore 121 and the lower core 122. The second stem 55 c is formed to beable to move inside of the upper core 121 and the lower core 122. Thespring retainer 125 for fastening the valve spring 51 is fastened to thesecond stem 55 c of the exhaust valve 8.

The electromagnetic drive device 120 includes a mover 129 which isfastened to the second stem 55 c. The mover 129 is arranged between theupper core 121 and the lower core 122. The mover 129 is formed by amagnetic substance. The exhaust valve 8 moves in the direction which isshown by the arrow 201. In the state where the upper coil 123 and thelower coil 124 are not electrified, the exhaust valve 8 closes due tothe biasing force of the valve spring 51. When opening the exhaust valve8, the lower coil 124 is electrified and the lower core 122 ismagnetized. The mover 129 is pulled to the lower core 122. The secondstem 55 c moves toward the combustion chamber side, whereby the exhaustvalve 8 can be opened. Note that, the electromagnetic drive device isnot limited to the above. Any electromagnetic drive device which enablesan on-off valve to be operated by magnetic force may be employed.

The combustion pressure control device in the present embodimentsuppresses the rise of the pressure of the combustion chamber 5 by thefluid spring 63 contracting and the tube-shaped member 61 and taperedplug part 55 a moving when the pressure of the combustion chamberreaches the control pressure. Furthermore, the combustion pressurecontrol device in the present embodiment can adjust the pressure of thecombustion chamber 5 by driving the electromagnetic drive device 120 inthe time period when the pressure of the combustion chamber 5 reachesthe control pressure.

The combustion pressure control device in the above embodiments isformed so that the coil spring 54 contracts when the pressure of thecombustion chamber reaches the control pressure and the tapered plugpart 55 a moves, but the invention is not limited to this. Thecombustion pressure control device can also be configured so that itdoes not include the coil spring 54 and so that the first stem 55 b andthe second stem 55 c are fastened to each other. That is, the stem mayalso be an integral piece. In this combustion pressure control device, aclearance is formed between the upper core 121 and the mover 129. Theclearance is formed larger than the amount of movement of the mover 129when the fluid spring 63 contracts. That is, the clearance is formed sothat the tapered plug part 55 a can freely move. When the pressure ofthe combustion chamber reaches the control pressure, the first stem 55 band the second stem 55 c move integrally in a direction away from thecombustion chamber. At this time, due to the fluid spring 63contracting, the pressure of the combustion chamber can be controlled.

FIG. 37 shows a graph of the pressure of the combustion chamber of aninternal combustion engine which is provided with the tube-shaped memberand the fluid spring etc. FIG. 37 is a graph of the pressure of thecombustion chamber of an internal combustion engine which is providedwith the first combustion pressure control device in, for example,Embodiment 1. When the pressure of the combustion chamber reaches thecontrol pressure, due to the delayed response of the combustion pressurecontrol device, sometimes overshoot occurs in the pressure of thecombustion chamber. When the fuel burns, the operation of the fluidspring 63 contracting and the movement of the tube-shaped member 61sometimes are delayed from the rise of the pressure of the combustionchamber 5. For this reason, sometimes the pressure of the combustionchamber 5 temporarily exceeds the control pressure.

Further, when the pressure of the combustion chamber falls from thecontrol pressure, due to the delayed response of the combustion pressurecontrol device, sometimes undershoot occurs in the pressure of thecombustion chamber. When the pressure of the combustion chamber fallsfrom the control pressure, the operation of the fluid spring 63extending and the movement of the tube-shaped member 61 are sometimesdelayed from the drop of the pressure of the combustion chamber. Forthis reason, sometimes the pressure of the combustion chamber 5temporarily excessively falls.

FIG. 38 is a time chart of the first operational control in thecombustion pressure control device of the present embodiment. At thetime of normal operation, in the time period when the pressure of thecombustion chamber reaches the control pressure, the upper coil 123 andthe lower coil 124 are not electrified. At the timing t1, the pressureof the combustion chamber reaches the control pressure. At thecombustion pressure control device of the present embodiment, the uppercoil 123 is electrified for a short time from the timing t1.Alternatively, it is electrified in a pulse manner. By electrificationof the upper coil 123, the upper core 121 is magnetized. The mover 129is pulled in a direction away from the combustion chamber. As a result,the force can be applied to the exhaust valve 8 in a direction where thevolume of the combustion chamber 5 becomes larger and the pressurebecomes smaller. For this reason, overshoot when the pressure of thecombustion chamber 5 reaches the control pressure can be suppressed.

Further, the pressure of the combustion chamber starts to fall at thetiming t2. In the first operational control of the present embodiment,the lower coil 124 is electrified for a short time from the timing t2.Alternatively, it is electrified in a pulse state. By electrifying thelower coil 124, the lower core 122 is magnetized. The mover 129 ispulled in a direction toward the combustion chamber. The force can beapplied to the exhaust valve 8 in a direction where the volume of thecombustion chamber 5 becomes smaller and the pressure of the combustionchamber 5 becomes larger. For this reason, undershoot can be suppressedwhen the pressure of the combustion chamber 5 starts to fall from thecontrol pressure. In this regard, when electrifying the lower coil 124so as to suppress undershoot, if the amount of electrification of thelower coil 124 becomes too large, the exhaust valve 8 is liable to open.For this reason, the lower coil 124 is preferably electrified by lessthan the amount of electrification by which the on-off valve opens.

In the present embodiment, the upper coil is electrified when thepressure of the combustion chamber reaches the control pressure.Further, the lower coil is electrified when the pressure of thecombustion chamber starts to decrease. The timing of electrification isnot limited to this. The upper coil can be electrified near the timingat which the pressure of the combustion chamber reaches the controlpressure. Alternatively, the lower coil can be electrified near thetiming at which the pressure of the combustion chamber starts todecrease.

FIG. 39 shows a time chart of the second operational control of thecombustion pressure control device in the present embodiment. In thesecond operational control, in the time period during which the pressureof the combustion chamber reaches the control pressure, the coil whichbiases the on-off valve in the direction toward the outside of thecombustion chamber is electrified. In the second operational control,the upper coil 123 is electrified from the timing t1 at which thepressure of the combustion chamber starts to rise in the compressionstroke to the timing t4 at which the pressure of the combustion chamberfinishes falling in the expansion stroke.

By electrifying the upper coil 123, the upper core 121 is magnetized.The mover 129 is pulled to the upper core 121. The mover 129 is biasedin a direction away from the combustion chamber. The exhaust valve 8 isgiven a biasing force in a direction where the volume of the combustionchamber 5 becomes larger. For this reason, the pressure of thecombustion chamber when the fluid spring 63 starts to contract, that is,the control pressure, can be lowered. For example, an operating statedetecting device can be used to detect the operating state and thecontrol pressure can be changed in accordance with the respectiveoperating states.

Further, by adjusting the amount of electrification which is applied tothe upper coil, the control pressure can be freely adjusted. Forexample, by increasing the amount of electrification which is applied tothe upper coil, the control pressure of the combustion chamber can belowered.

In the second operational control in the present embodiment, the uppercoil is electrified from the timing at which the rise of the pressure ofthe combustion chamber starts to the timing at which the fall of thepressure of the combustion chamber ends. The timing of electrificationis not limited to this. The upper coil can be electrified in a timeperiod of at least part of the time period at which the pressure of thecombustion chamber reaches the control pressure. For example, the uppercoil can be electrified in the time period from right before thepressure of the combustion chamber reaches the control pressure to rightafter the pressure of the combustion chamber starts to fall from thecontrol pressure.

In this regard, if electrifying in a time period other than the timeperiod at which the pressure of the combustion chamber reaches thecontrol pressure, if the amount of electrification of the upper coil istoo large, the magnetic force of the upper coil is liable to cause thetube-shaped member to move. For this reason, the amount ofelectrification of the upper coil is preferably less than the amount ofelectrification where the tube-shaped member moves.

FIG. 40 shows a time chart of the third operational control in thecombustion pressure control device in the present embodiment. In thethird operational control, control is performed to electrify the uppercoil right before the fluid spring extends and returns to its originalstate.

In the third operational control of the present embodiment, at thetiming t1, the tube-shaped member 61 moves in a direction away from thecombustion chamber 5 and the fluid spring 63 contracts. After this, thetube-shaped member 61 moves to the side heading toward the combustionchamber 5 and the fluid spring 63 extends. At the timing t2, thetube-shaped member 61 returns to its original position. At the timingt2, when the end part of the tube-shaped member 61 reaches the bottom ofthe engaging part 60 b of the frame member 60, sometimes noise andvibration are caused.

In the third operational control of the present embodiment, right beforethe end part of the tube-shaped member 61 reaches the engaging part 60 bof the frame member 60, the coil for biasing the exhaust valve 8 in theclosing direction is electrified. In the present embodiment, the uppercoil 123 is electrified in a short period right before the timing t2.Alternatively, it is electrified in a pulse manner. By performing thiscontrol, the speed when the tube-shaped member 61 reaches the bottom ofthe engaging part 60 b of the frame member 60 can be slowed and thenoise and vibration which occur when the tube-shaped member 61 reachesthe bottom can be suppressed. Further, the pressure of the combustionchamber can be kept from becoming unstable due to the vibration, etc.

In the third operational control of the present embodiment, the uppercoil is electrified right before the tube-shaped member reaches thebottom of the engaging part of the frame member, but the invention isnot limited to this. The upper coil may also be electrified during thetime period when the tube-shaped member is moving toward the combustionchamber. In this control as well, the speed of the tube-shaped memberwhen the tube-shaped member reaches the bottom can be reduced and noiseand vibration can be suppressed.

As shown in the first operational control to the third operationalcontrol, the combustion pressure control device in the presentembodiment can drive the electromagnetic drive device in the time periodwhen the pressure of the combustion chamber reaches the control pressureso as to adjust the pressure of the combustion chamber.

The rest of the configuration, actions, and effects are similar to thoseof Examples 1 to 3, so the explanations will not be repeated.

The above embodiments can be suitably combined. In the above figures,the same or corresponding parts are assigned the same reference signs.Note that, the above embodiments are illustrations and do not limit theinvention. Further, in the embodiments, are changes which are includedin the claims are intended.

REFERENCE SIGNS LIST

-   1 engine body-   4 cylinder head-   5 combustion chamber-   6 intake valve-   7 intake port-   8 exhaust valve-   9 exhaust port-   31 electronic control unit-   45 fuel property sensor-   51 valve spring-   54 coil spring-   55 a tapered plug part-   55 b first stem-   55 c second stem-   60 frame member-   61 tube-shaped member-   63 fluid spring-   64 pipe-shaped member-   64 b blocking member-   70 variable valve timing device 90, 91 exhaust cam 90 c, 91 c    recessed part-   95, 96 abutting part-   95 a, 96 a projecting part-   97 switching device-   120 electromagnetic drive device-   123 upper coil-   124 lower coil-   129 mover

1. An internal combustion engine provided with an on-off valve which hasa shaft-shaped part and tapered plug part and is formed to be able toopen and close a passage which is communicated with a combustionchamber, a support structure which includes a passage which communicateswith the combustion chamber and which supports the on-off valve, aninterposed member which is arranged in a region where the on-off valveis arranged in the passage which communicates with the combustionchamber and which is engaged with the tapered plug part of the on-offvalve at one end part which faces the combustion chamber, a springdevice for biasing the interposed member to the side which faces thecombustion chamber, an operating state detecting device which detects anoperating state of the internal combustion engine, and a movementrestricting device which restricts an amount of movement of theinterposed member, wherein the interposed member is formed to be able tomove substantially parallel to a direction of movement of the on-offvalve and abuts against the spring device at the other end part at theopposite side from the one end part, the spring device is formed so asto contract using a change in pressure of the combustion chamber as adrive source when the pressure of the combustion chamber reaches apredetermined control pressure, when the combustion chamber reaches thecontrol pressure during the time period from the compression stroke tothe expansion stroke of a combustion cycle, the spring devicecontracting causes the tapered plug part and the interposed member tomove toward the outside of the combustion chamber and the combustionchamber to increase in volume, and the engine detects the operatingstate of the internal combustion engine, selects a maximum pressure ofthe combustion chamber in accordance with the detected operating state,and uses the selected maximum pressure of the combustion chamber as thebasis to restrict the amount of movement of the interposed member. 2.(canceled)
 3. The internal combustion engine as set forth in claim 1,further provided with a blocking device which blocks at least part ofthe passage which communicates with the combustion chamber, wherein theblocking device is formed so as to promote a circumferential directionflow or an axial direction flow in the combustion chamber the smaller aflow sectional area of the passage which communicates with thecombustion chamber, and the smaller the flow sectional area of thepassage which communicates with the combustion chamber, the smaller themovement restricting device restricts the amount of movement of theinterposed member and the larger the maximum pressure of the combustionchamber is made.
 4. The internal combustion engine as set forth in claim1, wherein a plurality of on-off valves are arranged for a singlecombustion chamber, the engine is further provided with a plurality ofinterposed members and a plurality of spring devices which are arrangedcorresponding to the plurality of on-off valves, and the plurality ofspring devices are formed so that elastic forces become smaller thelarger the total weights of the moving members which include the taperedplug parts and the interposed members.
 5. The internal combustion engineas set forth in claim 1, wherein the shaft-shaped part of the on-offvalve includes a first valve shaft part which is connected to thetapered plug part and a second valve shaft part which is connected tothe first valve shaft part through an elastic member, and the elasticmember has an elastic force by which it contracts corresponding to theamount of contraction of the spring device when the pressure of thecombustion chamber reaches the control pressure and the spring devicecontracts and has an elastic force by which it does not contract whenopening the on-off valve for opening the passage which communicates withthe combustion chamber.
 6. The internal combustion engine as set forthin claim 1, further provided with a valve biasing member which biasesthe on-off valve in a direction by which the on-off valve closes,wherein the spring device is arranged at the inside of the valve biasingmember or at the outside so as to surround the valve biasing member. 7.The internal combustion engine as set forth in claim 1, further providedwith a cam for driving the on-off valve and a variable valve mechanismwhich changes a phase of the cam relative to a crank angle, wherein thecam has a recessed part which is formed so that the on-off valve canmove during the time period while the spring device is contracted, andthe variable valve mechanism is used to change the phase of the recessedpart of the cam so as to restrict the amount of movement of the on-offvalve during the time period while the spring device is contracted. 8.The internal combustion engine as set forth in claim 1, further providedwith an electromagnetic drive device for driving the on-off valve,wherein the electromagnetic drive device is driven during the timeperiod while the pressure of the combustion chamber reaches the controlpressure so as to adjust the pressure of the combustion chamber.